diff --git a/lib/CodeService.js b/lib/CodeService.js
index 8ddcea9..b2b11b4 100644
--- a/lib/CodeService.js
+++ b/lib/CodeService.js
@@ -68,7 +68,7 @@ class CodeService {
    * @returns {Promise.<undefined,Error>} A promise that returns nothing when
    *   resolved and returns an error when rejected.
    */
-  ensureValueSets(valueSetList = [], umlsUserName = env['UMLS_USER_NAME'], umlsPassword = env['UMLS_PASSWORD']) {
+  ensureValueSets(valueSetList = [], umlsUserName = env['UMLS_USER_NAME'], umlsPassword = env['UMLS_PASSWORD'], caching = true) {
     // First, filter out the value sets we already have
     const filteredVSList = valueSetList.filter(vs => {
       const result = this.findValueSet(vs.id, vs.version);
@@ -80,7 +80,7 @@ class CodeService {
     } else if ( typeof umlsUserName === 'undefined' || umlsUserName == null ||typeof umlsPassword === 'undefined' || umlsPassword == null) {
       return Promise.reject('Failed to download value sets since UMLS_USER_NAME and/or UMLS_PASSWORD is not set.');
     } else {
-      return downloadFromVSAC(umlsUserName, umlsPassword, filteredVSList, this.cache, this.valueSets);
+      return downloadFromVSAC(umlsUserName, umlsPassword, filteredVSList, this.cache, this.valueSets, caching);
     }
   }
 
@@ -93,9 +93,9 @@ class CodeService {
    * @param {string} umlsPassword - the UMLS password to use when downloading value sets (defaults to env "UMLS_PASSWORD")
    * @returns {Promise.<undefined,Error>} A promise that returns nothing when resolved and returns an error when rejected.
    */
-  ensureValueSetsInLibrary(library, checkIncluded = true, umlsUserName = env['UMLS_USER_NAME'], umlsPassword = env['UMLS_PASSWORD']) {
+  ensureValueSetsInLibrary(library, checkIncluded = true, umlsUserName = env['UMLS_USER_NAME'], umlsPassword = env['UMLS_PASSWORD'], caching = true) {
     const valueSets = extractSetOfValueSetsFromLibrary(library, checkIncluded);
-    return this.ensureValueSets(Array.from(valueSets), umlsUserName, umlsPassword);
+    return this.ensureValueSets(Array.from(valueSets), umlsUserName, umlsPassword, caching);
   }
 
   findValueSetsByOid(oid) {
diff --git a/lib/download-vsac.js b/lib/download-vsac.js
index d5b1cfe..dd8aef2 100644
--- a/lib/download-vsac.js
+++ b/lib/download-vsac.js
@@ -5,7 +5,7 @@ const mkdirp = require('mkdirp');
 const parseVSACXML = require('./parse-vsac');
 const debug = require('debug')('vsac'); // To turn on DEBUG: $ export DEBUG=vsac
 
-function downloadFromVSAC(username, password, input, output, vsDB={}) {
+function downloadFromVSAC(username, password, input, output, vsDB={}, caching=true) {
   var vsJSON = {};
   if (typeof(input) === 'string') {
     path.resolve(input);
@@ -21,7 +21,7 @@ function downloadFromVSAC(username, password, input, output, vsDB={}) {
   if (Object.keys(vsJSON).length > 0) {
     output = path.resolve(output);
     const oids = Object.keys(vsJSON).map(k => vsJSON[k]);
-    if (!fs.existsSync(output)){
+    if (caching && !fs.existsSync(output)){
       mkdirp.sync(output);
     }
     return getTicketGrantingTicket(username, password)
@@ -29,7 +29,7 @@ function downloadFromVSAC(username, password, input, output, vsDB={}) {
         const promises = oids.map(oid => {
         // Catch errors and convert to resolutions returning an error.  This ensures Promise.all waits for all promises.
         // See: http://stackoverflow.com/questions/31424561/wait-until-all-es6-promises-complete-even-rejected-promises
-          return downloadValueSet(ticketGrantingTicket, oid, output, vsDB)
+          return downloadValueSet(ticketGrantingTicket, oid, output, vsDB, caching)
             .catch((err) => {
               debug(`Error downloading valueset ${oid}`, err);
               return new Error(`Error downloading valueset: ${oid}`);
@@ -41,7 +41,7 @@ function downloadFromVSAC(username, password, input, output, vsDB={}) {
         const errors = results.filter(r => r instanceof Error);
         if (results.length - errors.length > 0) {
         // There were results, so write the file first before resolving/rejecting
-          return writeFile(path.join(output, 'valueset-db.json'), JSON.stringify(vsDB, null, 2))
+          return writeFile(path.join(output, 'valueset-db.json'), JSON.stringify(vsDB, null, 2), caching)
             .then(
               (result) => errors.length == 0 ? result : Promise.reject(errors),
               (err) => { errors.push(err); return Promise.reject(errors); }
@@ -66,14 +66,14 @@ function getTicketGrantingTicket(username, password) {
   return rpn(options);
 }
 
-function downloadValueSet(ticketGrantingTicket, oid, output, vsDB={}) {
+function downloadValueSet(ticketGrantingTicket, oid, output, vsDB={}, caching=true) {
   return  getServiceTicket(ticketGrantingTicket)
     .then((serviceTicket) => {
       return getValueSet(serviceTicket, oid);
     })
     .then((data) => {
       parseVSACXML(data, vsDB);
-      return writeFile(path.join(output, `${oid}.xml`), data);
+      return writeFile(path.join(output, `${oid}.xml`), data, caching);
     });
 }
 
@@ -96,18 +96,22 @@ function getValueSet(serviceTicket, oid) {
   return rpn(options);
 }
 
-function writeFile(file, data) {
+function writeFile(file, data, caching=true) {
   return new Promise((resolve, reject) => {
-    debug('Writing:', file);
-    fs.writeFile(file, data, (err) => {
-      if (typeof err !== 'undefined' && err != null) {
-        debug('Error writing file', file);
-        reject(err);
-      } else {
-        debug('Wrote file', file);
-        resolve(file);
-      }
-    });
+    if (caching) {
+      debug('Writing:', file);
+      fs.writeFile(file, data, (err) => {
+        if (typeof err !== 'undefined' && err != null) {
+          debug('Error writing file', file);
+          reject(err);
+        } else {
+          debug('Wrote file', file);
+          resolve(file);
+        }
+      });
+    } else {
+      resolve();
+    }
   });
 }