A group of 295 Israeli infantry recruits was evaluated in a prospective study of stress fractures which began in basic training. On the basis of scintigraphy, 91 of the recruits (31%) were found to have sustained stress fractures during basic training. Sixty-six of the 91 recruits with stress fractures (72%) were followed for a minimum of 1 year after basic training to determine the natural history of a soldier who sustains a stress fracture and resumes training after a period of rest. Five clinical patterns were observed: (1) uneventful recovery (47%); (2) protracted recovery (13.6%); (3) symptoms consistent with recurrent stress fractures in new sites (19.6%); (4) intermittent nonstress fracture bone pain (16.7%); and (5) chronic stress fractures (3%). The incidence of recurrent stress fractures was 10.6%. A control group of 60 recruits who sustained no stress fractures in basic training had a 1.7% incidence of stress fractures after basic training. Recruits who sustained stress fractures in basic training continued to be a higher risk for stress fractures during subsequent training.