So how long without lesions showing up on an MRI? About eight years for me.

My presenting symptom was Peripheral Neuropathy. I was told it was ideopathic for a few years until my neuro noticed that my reflexes were getting more brisk. Since that was not normal for PN, he sent me to a MS neuro who told me that the lesions that showed up in my spine were "normal" and come back in 6 months. I had a remission and got my general practitioner to prescribe another MRI (again with contrast) and no lesions were found. I took both MRIs to a third neuro and she said that I had MS (duh!). Lesions that come and go are MS. The second neuro also did a Lumbar Puncture (spinal tap) but it didn't show any Obands. That is not unusual with mild MS.

So that is my history and I have had only one MRI since. It showed no lesions. I had the MRI done because I was having extra heavy balance problems. Currently I have all of the fatigue and balance problems in addition to my peripheral neuropathy (demylination of the nerves in my feet).

I've heard of some people who have yearly MRIs but they usually have severe or primary progressive MS.

I've been on Betaseron since I was diagnosed by neuro number three. Still go in 2X a year to neuro but no MRIs. Hope this answers your question.