Athletic injuries of the foot and lower extremity are commonly treated with custom foot orthoses. These devices usually provide immediate relief of the athlete's pain and dysfunction. Occasionally, however, they do not help, or even increase the patient's discomfort. We discuss a method of using in-shoe pressure-measurement systems to analyze the athletic patient's foot and lower-extremity function before and after treatment with custom foot orthoses, with a focus on sagittal plane biomechanics. Case histories are presented of athletes whose gait pathologies were identified and treated successfully using an in-shoe pressure-measurement system.