Over the post 10 years 231 insufficiency fractures of the sacrum have been reported in the literature. These fractures, which are due to osrteopenia, form a distinct subgroup of pathologic fractures. In 1.8% (n = 20) of the oldr-than-55-years female patients (total = 1,015) admitted to the authors' Rheumatology department between 1939 and 1991, a fracture of the sacrum was diagnosed In all cases the diagnosis was confirmed with computed tomography. Frequency, age, sex, diagnosis, underlying diseases, and associated fractures of the 20 cases of in sufficiency fractures of the sacrum are described and compared with those previously reported. Insufficiency sacral fracture at a cause of low-back pain in women older than 55 years of age is concluded to be a clinical entity.