Three women with hypoparathyroidism are described who developed severe symptomatic hypercalcaemia while being treated with alphacalcidol (1 alpha-hydroxycholecalciferol; One-Alpha). One sustained permanent renal damage. Alphacalcidol may have advantages over calciferol in its speed of action but poisoning may be more likely to occur. Frequent follow-up checks on the plasma calcium is needed for any patient on alphacalcidol. For long-term management calciferol may still be the drug of choice.