The incidence and significance of concomitant groin hernias were evaluated in a prospective study of 278 adult patients with an inguinal or femoral hernia. The material was collected in the three years 1975--77 and consisted of 290 electively operated groin hernias. The incidence of various combinations of primary inguinal and femoral hernias was 14%. Three of the 37 recurrent hernias (8%) were evidently caused by a concomitant hernial sac missed in the first operation.