BACKGROUND: Vitamin D deficiency is common and predisposes to many serious diseases, yet often goes unrecognized. FINDINGS: We describe a case of severe vitamin D deficiency with osteomalacia in a patient resident in a psychiatric hospital for more than 35 years, and discuss causes and complications. We assayed the serum 25-hydroxyvitamin D levels of all patients under our care on one old-age psychiatry rehabilitation unit. Ten of twelve (83%) of patients had vitamin D deficiency, and 92% had suboptimal vitamin D levels. Vitamin D status was strongly predicted by dietary supplementation. Of those not on vitamin D supplements, 100% had vitamin D deficiency, with vitamin D levels significantly below those of historical controls. Age, sex, and duration of admission did not predict vitamin D status in this group. CONCLUSION: We advocate vitamin D screening in all patients admitted to psychogeriatric units, and discuss treatment options given the current problems affecting high-dose vitamin D supply to the United Kingdom.