While the main syndrome of tetany arising from hypoparathyroidism is widely recognized, it is doubtful if a sufficiently comprehensive view has been taken of the extensive range of manifestations which may be presented. The underlying pathological mechanisms may also be complex, and the circumstances under which hypoparathyroidism may develop are not always self-evident. Lyle (1949) attempts to classify hypoparathyroidism on an aetiological basis, and distinguishes postoperative, intrinsic, extrinsic, and idiopathic types. In our paper we are mainly concerned with tetany following thyroidectomy, the incidence of which has been estimated by Bell and Bartels (1951) as 2·9 per cent., based on their observations of 2,000 consecutive operations. The case which we are going to describe is one in which a history of thyroidectomy did not immediately appear significant in relation to the presenting features. Admission to hospital followed the onset of a psychotic illness, which in itself did not indicate any underlying organic disturbance, despite an account of an occasional epileptic attack some time previously. The latter feature, however, led to routine E.E.G. investigations. These are of particular interest in this case, especially as some of the recordings had been made before the diagnosis of hypoparathyroidism was established, and before the significance of the fits in the clinical syndrome was appreciated.