Vitamin D deficiency is common in patients with insufficient sunlight exposure and nutritional deficit in calcium and vitamin D. We present a patient with vitamin D deficiency, secondary hyperparathyroidism and resulting osteoporotic fractures caused or supported by psychosis-induced minimal sunlight exposure and nutritional deficits. To our knowledge, this is the first case where delusional ideas could have led to a vitamin D deficiency, secondary hyperparathyroidism and osteoporotic fractures. Similar clinical cases could be more often, but significantly underdiagnosed, among schizophrenia patients. An appropriate prevention by UV light exposure, food fortification and supplements is normally sufficient for patients at risk.