Physical training is a significant element of Marine Corps basic training which may affect nonfitness basic training outcomes in addition to improving fitness. If so, physical training side effects should be considered when designing and evaluating physical training programs. This study capitalized on naturally occurring platoon differences in fitness outcomes to classify basic training platoons into relatively high and low improvement groups. The high improvement group had better attitudes toward the Marine Corps, greater perceived self-improvement, and performed better during basic training. The groups had comparable illness rates during basic training, but there was more medical attrition and overall attrition in the high improvement group. The groups did not differ with regard to Fleet Marine Force promotion or attrition rates. These findings demonstrate that physical training programs may indeed influence nonfitness basic training outcomes. Additional research is needed to verify that physical training differences actually cause nonfitness basic training outcomes, to determine whether these side effects are large enough to be of practical importance, and to identify specific aspects of physical training programs that are important for promoting nonfitness basic training objectives. (Author)