The session below shows how to create a document that is close to the maximum size and then retrieve it with an aggregation command (using a cursor) and with a findOne(). The aggregation fails. MongoDB shell version: 2.5.3 connecting to: test Server has startup warnings: 2013-11-03T19:16:05.526-0500 [initandlisten] 2013-11-03T19:16:05.526-0500 [initandlisten] ** NOTE: This is a development version (2.5.3) of MongoDB. 2013-11-03T19:16:05.526-0500 [initandlisten] ** Not recommended for production. 2013-11-03T19:16:05.526-0500 [initandlisten] // As big a document as we can make. > var bytes=(16 * 1024 * 1024) - (4 + 6 + 5); // ... using one large hex string. > var hex="" > for ( var i = 0; i < bytes; ++i ) { hex=hex+"00"; } ; db.test.insert( { "_id" : HexData( 0, hex ) } ) > db.test.find({}, { _id : 0 } ) { } > db.test.aggregate( { $match : {} } ) assert: command failed: { "errmsg" : "exception: Tried to create string longer than 16MB", "code" : 16493, "ok" : 0 } : aggregate with cursor failed Error: Printing Stack Trace at printStackTrace (src/mongo/shell/utils.js:38:15) at doassert (src/mongo/shell/assert.js:6:5) at Function.assert.commandWorked (src/mongo/shell/assert.js:238:5) at DBCollection.aggregate (src/mongo/shell/collection.js:907:12) at (shell):1:9 2013-11-03T19:23:27.549-0500 command failed: { "errmsg" : "exception: Tried to create string longer than 16MB", "code" : 16493, "ok" : 0 } : aggregate with cursor failed at src/mongo/shell/assert.js:7   // Verify we can read the document without printing it out... > Object.bsonsize( db.test.findOne({}) ) 16777216