Like Dr. Mom says, it varies by school. At KCUMB, we get a full summer vacation after MSI year, although if you want to, you can do a preceptorship. MSII year goes from early August until the end of the following July. We had about a month off before MSIII clinical rotation began, and these go all the way to next August, when I think we have a few weeks off. MSIV year starts again in September, and ends in May. No such thing as summer vacation after that!