This report documents a prospective study of effects of four sole constructions for combat boots on the incidence of lower extremity overuse injuries among men and women undergoing U.S. Army basic combat training. Trainees were issued boots that had identical uppers, but differed in soling system constructions. The constructions tested were direct-molded (DMS), welt (WLT), injection-molded, direct-attach with a solid rubber outsole (A-R), and injection-molded, direct-attach with a polyurethane outsole (A-P). The study sample, 1,028 men and 388 women, was randomly divided into four sole construction groups. Group assignment determined the type of boots issued for wear during 10 weeks of basic training. The principal source of data was sick call visits made for problems experienced at or below the knee. Analyses of the men s data revealed that the percentage attending at least one sick call was unaffected by the type of sole construction worn; the proportion of women attending at least one sick call for a problem at or below the knee was highest in the A-P group and lowest in the A-R group. Analyses of medical diagnoses of overuse injuries of the lower extremities did not reveal differences among sole construction groups for the men s data, but the women s data indicated that the proportion of overuse injuries was highest in the A-P group. Based upon overall study results, the A-P construction should not be considered further as a soling system for Army boots, but the A-R construction is acceptable.