1)All DO students must take the COMLEX in order to graduate. It makes no difference if they are 100% certain they want to pursue an allopathic residency program or not.Most DO schools are now requiring their students to have passed both step 1 and 2 of the COMLEX to graduate. In addition many require successfull passage of COMLEX step 1 in order to be allowed to go on to 3rd and 4th year rotations. Hence, while the USMLE is an option, the COMLEX isn't. It must be taken.
2) Most allopathic residency programs do not require the USMLE from DO applicants. Programs in certain geographical areas, with a small number of practicing DOs, are still reluctant to accept the COMLEX. Lousiana is the only state that only accepts the USMLE, so a DO gradaute wanting to apply to a residency program in LA must have taken BOTH the COMLEX and the USMLE. Very competitive allopathic programs may also frown upon candidates who have only the COMLEX, often simply because they are not familiar on how to compare the results from these two tests.
3) Many DO students choose to take the USMLE in addition to the COMLEX, in order to leave their options open, if they happen to end up wanting to apply to one of the programs that prefers them to have USMLE scores too. About 100 students in my class (out of 226) have taken the USMLE so far, and another 10 or so are taken it this month. The passing rate was slightly above 95%. Thus, although DO students are specifically prepared to take the COMLEX, they are not doing too shabbily when it comes to taking the USMLE either.
