Obsessive-compulsive neurosis: two identical twin pairs.

Two pairs of monozygotic twins concordant for obsessive-compulsive neurosis are described. In each the proband and co-twin developed their symptoms independently and without prior knowledge of the other's illness. Despite this there was a marked similarity of symptoms within each pair. The existence of these and other pairs reported elsewhere, strongly suggests that familial and possibly genetic factors contribute to the aetiology of the disorder.