Atelosteogenesis I (AT-I) and Boomerang dysplasia have been described as separate lethal bone dysplasias. The possibility of a common cause of both conditions was suggested by Hunter and Carpenter (Clin Genet 39(6): 471-480, 1991) in their report of a patient with apparent manifestations of both AT-I and Boomerang dysplasia. We report on a male fetus of 31 weeks gestation whose clinical, radiologic and histologic findings are compared to reported cases of AT-I, Boomerang dysplasia and the patient of Hunter and Carpenter (Clin Genet 39(6): 471-480, 1991). From the documentation of clinical and radiologic findings we demonstrate overlap of AT-I and Boomerang dysplasia in our patient, and, from histologic examination, suggest a defect of cartilage and bone formation as the basic abnormality in this lethal bone dysplasia.