We describe the case of a 56-year-old man with rapidly progressive osteoporosis culminating in pathologic fractures of multiple lumbar vertebrae. With the exception of discrete brown-reddish cutaneous lesions, low back pain was the only prominent symptom. Laboratory evaluations excluded metabolic or endocrinological abnormalities. Serum tryptase was highly increased, as was urinary excretion of histamine. Iliac crest biopsy demonstrated mastocytosis, which was confirmed by skin biopsy and which was consistent with teleangiectasia macularis eruptiva perstans, a rare form of cutaneous mastocytosis. In cases of unusually marked osteoporosis, especially in men, mastocytosis should be considered in the differential diagnosis.