diff --git a/src/main.ts b/src/main.ts
index 1e73f241e..bc862ac33 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -32,7 +32,7 @@ export function activate(context: vscode.ExtensionContext): any {
     ensureRuntimeDependencies(extension, logger, reporter)
         .then((success : boolean) => {
             // activate language services
-            OmniSharp.activate(context, reporter);
+            OmniSharp.activate(context, reporter, _channel);
 
             // register JSON completion & hover providers for project.json
             context.subscriptions.push(addJSONProviders());
diff --git a/src/omnisharp/extension.ts b/src/omnisharp/extension.ts
index eb13b2598..0c3186af8 100644
--- a/src/omnisharp/extension.ts
+++ b/src/omnisharp/extension.ts
@@ -30,7 +30,7 @@ import { addAssetsIfNecessary, AddAssetResult } from '../assets';
 import { sum, safeLength } from '../common';
 import * as utils from './utils';
 
-export function activate(context: vscode.ExtensionContext, reporter: TelemetryReporter) {
+export function activate(context: vscode.ExtensionContext, reporter: TelemetryReporter, channel: vscode.OutputChannel) {
     const documentSelector: vscode.DocumentSelector = {
         language: 'csharp',
         scheme: 'file' // only files from disk
@@ -88,6 +88,25 @@ export function activate(context: vscode.ExtensionContext, reporter: TelemetryRe
         }));
     }
 
+    // After server is started (and projects are loaded), check to see if there are
+    // any project.json projects. If so, notify the user about migration.
+    disposables.push(server.onServerStart(() => {
+        utils.requestWorkspaceInformation(server)
+            .then(workspaceInfo => {
+                if (workspaceInfo.DotNet && workspaceInfo.DotNet.Projects.length > 0) {
+                    const shortMessage = 'project.json is no longer a supported project format for .NET Core applications.';
+                    const detailedMessage = "Warning: project.json is no longer a supported project format for .NET Core applications. Update to the latest version of .NET Core (https://aka.ms/netcoredownload) and use ‘dotnet migrate’ to upgrade your project (see https://aka.ms/netcoremigrate for details).";
+                    const moreDetailItem: vscode.MessageItem = { title: 'More Detail' };
+
+                    vscode.window.showWarningMessage(shortMessage, moreDetailItem)
+                        .then(item => {
+                            channel.appendLine(detailedMessage);
+                            channel.show();
+                        });
+                }
+            });
+    }));
+
     // Send telemetry about the sorts of projects the server was started on.
     disposables.push(server.onServerStart(() => {
         let measures: { [key: string]: number } = {};