Among 1685 patients who sustained a hip fracture at the island of Crete (Greece) in a 4-year period we found 106 patients with bilateral noncontemporary hip fractures. Pathologic hip fractures and fractures that emerged from high energy trauma were excluded. To investigate the possible factors predisposing to the later fracture in the sound hip, we studied these 106 patients and compared them with the 1579 patients who sustained a single hip fracture (control group). There was no significant difference between the mean age of the bilateral group at the time of the first hip fracture (78.3 +/- 7.4 years, range 52-94 years) and the mean age of the control group (77.3 +/- 11.9 years, range 50-101 years). We found no significant difference in the bone status between the two groups, using both lumbar spine dual photon absorptiometry (DXA) and calcaneus broadband ultrasound attenuation (BUA). Falls, which were the main cause of all the hip fractures, were much more common in the bilateral group. The second hip fracture was of the same location (trochanteric or cervical) in 92% of the trochanteric and 68% of cervical fractures and a tendency to greater displacement or instability was observed. Of the second hip fractures 75% happened in the first 48 months after the first one. The mean interval time was much longer (160 months) when a neck fracture was followed by a trochanteric one.