The medical records of 176 patients with an isolated diagnosis of fatigue were reviewed. The study population represented the experience of 4 family physicians in private practice and of residents and staff of a university family medicine center in Denver, Colorado, USA, over a 12 mo. period. Variables included for study were age, sex, family structure, diagnostic testing, duration of symptoms and associated final diagnosis. Women outnumbered men in the study population 2:1. Fatigue occurred most frequently in people aged 15-34 yr. Single men and women were represented in the study population at a higher rate than family members. Single women tended to have physical diagnoses associated with their fatigue, while women who were members of family units tended to have psychological diagnoses associated. Fatigue lasting > 4 mo. was more frequently associated with psychological problems, while symptoms < 4 mo. were more frequently associated wtih physical problems. Physical problems were involved in just over half the cases, with the most common being the prolonged viral syndrome. A discussion with the patient regarding fatigue and its origin was documented in about half of the cases.