Cri-du-chat syndrome (5p-) is one of the most frequently occurring chromosomal deletion syndromes in man. Clinical findings have been described extensively in literature, but documentation of the patients' mental development has been poor. Recently the clinical heterogeneity and variance in psychomotor development was studied in a large series of patients. Review of the literature revealed that some 15% of the cases were found to be familial, there appears to be a slight correlation between karyotype and phenotype and the positive effects of early stimulation programs on the patients' prognosis is pointed out. Some 60% of the patients need regular medical care and nearly all are mentally retarded. However a wide spectrum of developmental abilities is displayed and a number of patients can be reared at home for several years. Life expectancy depends on the number and severity of birth defects.