Of the potential health risks of silicone breast implants it is the concern about implant durability, life span and the possible association with connective tissue disease which has attracted most attention. A prospective study addressing these factors was therefore undertaken over an 11 month period. 51 patients presenting with significant capsular contracture, suspected prosthesis rupture or unrelieved implant-induced anxiety underwent revisional breast surgery after biochemical, haematological and immunological screening. Of these 51 patients (83 breasts), 14 (19 breasts) had ruptured implants (23% incidence). These were all smooth prostheses belonging to a cohort manufactured more than 10 years ago; their mean in situ duration being 12 years vs. 5.5 years for the intact group (p = 0.0024; Kruskal-Wallis one-way ANOVA). There were no systemic complications from implant rupture and the mean blood silicon level was normal. One patient with pre-existing pernicious anaemia had elevated autoantibodies. The mean ESR in the ruptured implant group was 6 mm/hour. It is concluded that rupture of breast implants is not as uncommon as hitherto thought and is strongly correlated with their in situ duration. In this study implant gel leakage was not associated with serious systemic effects.