From 1992 to 1996, 189 saline breast implants were inserted into patients (54 for breast augmentation and 135 for replacement of explanted silicone gel implants). Nine implants (4.8%) underwent spontaneous deflation at a mean of 2.8 months postoperation (range, 0.5 to nine months). Six deflations were partial (10% to 50% of implant volume), and three were complete. All failed implants were from the same manufacturer and had the same leaf valves. None of the failed implants demonstrated any visible defects in their walls or valve mechanisms when examined in the operating room. However, subsequent analyses indicated that all failed implants demonstrated a slow leak through the leaf valve mechanism - as slow as two to three drops per 12 h. This rate increased significantly when pressure was applied to the implant. In the three implants with delayed leakage (six to 10 months), fibrous tissue was observed in the leaf valve mechanism of the implants. It is postulated that failure of all nine implants resulted because of defects in their valves and that fibrous tissue ingrowth into the leaf catheter valve mechanism may have played a role in at least three. The tissue may have provided a 'wick' to stimulate fluid leakage. The use of these leaf valve implants was discontinued one year ago. Since then, no failures have been observed in any of the 68 diaphragm valve implants that have been inserted during the past year.