Although calcification of the basal ganglia is a relatively common and asymptomatic finding on cranial computed tomography, familial idiopathic calcification of the basal ganglia (ICBG) is a rare disorder with neurological and behavioral manifestations. Attention has recently been drawn to the frequency with which cases are diagnosed as schizophrenic (Cummings et al. 1983; Lowenthal, 1986; Davison, 1987). We report a family in which a mother and son have ICBG, but while the son has a paranoid schizophrenia and intellectual deterioration, the mother shows no psychiatric illness. A review of the relevant literature suggests that psychosis is not as common as usually supposed, and may only be coincidentally associated with familial ICBG. Moreover, we find little convincing evidence that familial ICBG is an independent entity; instead, and in agreement with earlier authorities (Bruyn et al. 1964), we argue that published accounts and our own cases provide evidence that the condition is related to pseudo-hypoparathyroidism (PHP) and, therefore, may be due to a defect in a guanine nucleotide binding protein.