This study retrospectively identifies and characterizes patients with facial palsy related to birth trauma and describes the natural history of this disorder. The records of infants born with facial weakness or paralysis over a 5-year period at Brigham and Women's Hospital were reviewed, and criteria were defined to assign a diagnosis of acquired facial palsy based on birth history and documented physical examinations. The majority of patients were followed up by interview with a family member. Among 44,292 infants born between October 1, 1982 and July 31, 1987, there were 92 recorded cases of congenital seventh nerve palsy. Of these, 81 were acquired, for an incidence of 1.8 per 1000. Seventy-four of the 81 (91 percent) were associated with forceps delivery. By contrast, obstetric forceps were used in 19 percent of all deliveries during the period of the study. The average weight of subjects was 3.55 kg, versus a mean overall birth weight of 3.23 kg. Fifty-nine percent of mothers of affected children and 37 percent of controls were prima gravidas. Forceps delivery, birth weight of 3500 gm or more, and primiparity were all significant risk factors for acquired facial palsy. The incidence of additional birth injuries also was substantially higher among affected subjects than among the general population of newborns. Sixty-six of 81 patients had adequate follow-up. Recovery has been complete for 59 patients (89 percent) and incomplete for the remaining 7 (mean follow-up 34 months). In summary, congenital traumatic facial palsy has definable risk factors and a predictably favorable outcome.