How often should I do pilates?

I personally think a maximum of 3 a week would be sufficient as long as they are spread out and not on consecutive days, to give your body time to recover. A few people I know do pilates once a week which is better than none, as long as they are doing some other form of exercise, but from a pilates point of view, you won't improve. You would almost certainly risk DOMS (delayed onset muscle soreness) and you wouldn't progress. I would recommend twice a week and you should notice a difference after 6 weeks. I like to mix my sessions up so we are working a different group of muscles each time. I have heard of instructors using the same lesson plan for 3 months, but all that means you are working the same muscles and neglecting the rest. A good mix of exercises is best in my opinion.