The risk factors associated with 34 deep infections from a consecutive series of 803 total hip replacements have been analysed using standard actuarial methods. The follow-up ranged from 3 to 10 years. Absence of prophylactic antibiotics, complications after operation, discharging wounds, previous operations and remote infection were related to the development of deep periprosthetic infection. An early discharge from the wound with growth of micro-organisms, though superficial in appearance, proved to be associated with a high risk of developing late deep infection. The mechanisms associated with deep infection involved multiple interrelated risk factors. Multiple regression analysis of our data indicated that these risk factors, when acting together, potentiate their effect on the development of the deep infection.