X-linked hydrocephalus is a variable condition caused by mutations in the gene encoding for L1CAM. This gene is located at Xq28. Clinically the spectrum ranges from males with lethal congenital hydrocephalus to mild/moderate mental retardation and spastic paraplegia. Few carrier females show minimal signs of the syndrome. Although most cases are familial, de novo situations have been reported. We report two new families with the syndrome and a L1 mutation. Family 1 has two patients and family 2 a single patient. Clinical diagnosis in all three affected boys was beyond doubt. Prenatal testing through chorionic villus biopsy is possible only with a demonstrated L1 mutation. In lethal sporadic cases neuropathology is very important in order to evaluate for features of the syndrome. We stress the importance of further clinical reports including data on neuropathology and DNA analysis in order to further understand the mechanisms involved in this disorder.