Letters of Recommendation - Duration Etiquette I finished my undergraduate degree in mathematics about two years ago, and started a master's program last year. Now that I am about half way through the MS program, I am convinced that I want to get into a doctoral program. I was admitted to the master's program based upon very strong recommendations from respected scientists at the university where my undergraduate degree was obtained.  

The MS program I am attending is at a small, noncompetitive institution. I am thinking that recommendation letters from this school would not be as meaningful. Also, based upon the limited scope of the research being conducted here, and my limited capacity to participate, I fear that letters from these professors might not be as strongly worded.

It is my intention to apply to several programs starting in December of this year. My question is this: Is it unreasonable to ask for my old references to "re-send" their letters of recommendation, almost 3 years after my association with them has concluded? Would it seem peculiar to the admissions board if all of my recommendation letters came from a school other than the one where I (will) have completed my MS?
It would be normal to have some letters of recommendation from professors at your undergraduate institution.  In my experience, faculty often write such letters for students a few years after they've graduated and will typically keep old letters of recommendation on file as a starting point for an updated letter.  

However, it is also important to have positive letters of recommendation from your current advisor and possibly others at your current institution.  If you don't get such recommendation letters, then this could be taken as a sign that you've done badly at your current institution.