Malignant osteopetrosis (MOP) is an autosomal recessive disease in which osteoclast dysfunction results in excessive bone deposition and early infant death. Thirteen children suffering from MOP from four related families all belonging to one Bedouin tribe, were studied. The disease was diagnosed as early as at a few days postnatal to 5 months. Nine children underwent BMT, four of whom are still alive; one is blind and two have markedly reduced vision. Four children who did not undergo BMT died between 4 and 6 months of age. Recently, the gene for MOP has been mapped for this Bedouin tribe allowing prenatal diagnosis. Seven pregnancies were subsequently prenatally diagnosed and two fetuses were found to be affected. Pregnancy was electively terminated in one case. In the other case the parents refused and after establishing the diagnosis, the newborn was transplanted at the age of 7 days.