Ninety-one infants who sustained a brachial plexus birth injury were treated with only physical and occupational therapy. The children were evaluated at 3-month intervals and followed for a minimum of 2 years. Sixty-three children with an upper or upper-middle plexus injury recovered good to excellent shoulder and hand function. In all of these children, critical marker muscles recovered M4 by 6 months of age. Twelve infants sustained a global palsy, with critical marker muscles remaining at M0-M1 at 6 months, resulting in a useless extremity. Sixteen infants with upper and upper-middle plexus injuries failed to recover greater than M1-M2 deltoid and biceps by 6 months, resulting in a very poor final outcome. These data provide useful guidelines for selection of infants for surgical reconstruction to improve ultimate outcome.