Seventy-four patients with premature union of the lambdoid suture were treated at The Hospital for Sick Children during the years 1972 through 1982. Lambdoid synostosis is considered to be a rare form of craniosynostosis, but this is more likely due to lack of recognition rather than to infrequent occurrence. The skull deformity resulting from lambdoid synostosis is often mistakenly attributed to positional molding rather than to actual synostosis. When the lambdoid suture closes, the occiput on the involved side is flat, the forehead on the same side tends to bulge forward, and the ear on this side adopts a low and forward position. Skull x-ray films may demonstrate obliteration of the lambdoid suture, but more frequently one sees sclerosis along one edge of the closing suture. Radionuclide bone scanning will show increased activity during the active phase of union and decreased or absent activity once union has occurred. Craniectomy performed during the neonatal period will correct the deformity and provide for normal cranial growth. Delay in surgery beyond 6 months will frequently necessitate a more extensive cranial repair.