Bone mineral density (BMD) and hip axis length (HAL) are important determinants of fracture risk in women. There are, however, few data concerning their predictive risk in men. The aim of this study was to determine the relationship between BMD, HAL and the risk of hip fracture in men. A case-control design was used. Cases were men aged 50 years and over with a minimal-trauma hip fracture admitted to the Royal Cornwall Hospital, Truro, during 1995-1997. Controls were recruited from a large general practice within the catchment area of the hospital. Subjects were invited for assessment of BMD at the lumbar spine and proximal femur, using dual-energy X-ray absorptiometry. HAL was assessed using machine software. Data concerning BMD were available in 62 fracture cases and 100 controls. After adjusting for age, height and weight, a reduction in BMD was associated with a significant increase in the risk of hip fracture [odds ratio (OR) 1.8-4.0 per standard deviation (SD) reduction, depending on site]. HAL was similar in both fracture and control groups (12.0 cm vs 12.0 cm). After adjusting for height, there was no association between HAL and the risk of hip fracture (OR per 1 SD increase in HAL = 0.9; 95% confidence interval 0.6, 1.3). Compared with those with a cervical fracture (n = 31), those with an intertrochanteric fracture (n = 31) had lower BMD at all skeletal sites, though this was significant for the trochanteric site only. It is concluded that BMD though not hip axis length is a risk factor for low-trauma hip fracture in Caucasian men.