OBJECTIVE Risk factors of obstetrical brachial plexus palsy include: (1) large birth weight, (2) shoulder dystocia and prolonged second stage of labour, (3) instrumental vaginal delivery (forceps delivery, vacuum extraction), (4) diabetes mellitus and mother's obesity, (5) breech presentation, (6) delivery and infant with obstetrical brachial plexus palsy in antecedent delivery. The purpose was analysis of the classical risk factors for brachial plexus palsy based on our own clinical material. METHODS Clinical material consists of 83 children with obstetrical brachial plexus palsy treated at the Department of Trauma and Hand Surgery (surgically--54, conservatively--29). Control group consists of 56 healthy newborns. Data recorded included: birth weight, body length, head and chest circumference, Apgar test at 1 min., type of brachial palsy and side affected, type of birth, presentation, duration of delivery (II stage), age of mother, mother's diseases, parity. RESULTS The infants treated surgically have had a significantly higher birth weight, body height, head and chest circumference, in compression with control group and group treated conservatively. The differences were statistically important. Shoulder dystocia occurred in 32.9% of all vaginal delivery. Instrumental vaginal delivery was observed in 11.3% and breech presentation in 4.9% cases. There were no incidences of obstetrical brachial plexus palsy recurrence. Diabetes mellitus and mother's obesity was found in 3 cases. CONCLUSIONS (1) Fetal macrosomia is the important risk factor of the obstetrical brachial plexus palsy. (2) Obstetrical brachial plexus palsy may occur also in the absence of the classical risk factors.