I've been asked couple of times (by clients, eMail and also here in comments ) about maximum size for Silverlight Isolated Storage. From tests I did, seems that maximum quota size is theoretically limited by total of long.MaxValue number of bytes. 1: // Request more quota space. 2: if (!store.IncreaseQuotaTo( long .MaxValue)) 3: //if (!store.IncreaseQuotaTo(store.Quota + spaceToAdd)) 4: { 5: // The user clicked NO to the 6: // host's prompt to approve the quota increase. 7: tbResults.Text...