Complications after procedures performed by residents are thought to occur most often early in the first postgraduate year (PGY-1). We evaluated the number of pneumothoraces (PTXs) caused by central venous line insertion (CVLI) by two groups of PGY-1 residents in both the first 3 months of residency and the entire year from 1996 through 2000 to determine the impact of CVLI training on PTX. From 1996 through 1998 fourth-year medical students had no specific training in CVLI and learned on the job as residents. Starting with the Class of 1999 we replaced this approach with a structured program in CVLI. Didactic sessions detailing anatomy and technique were followed by skill performance in a fresh cadaver model. Students performed skills initially under the direct supervision of a faculty member, who provided immediate feedback. Videotapes of this performance were reviewed with the students by both surgeons and kinesiologists to correct deficits before repeat sessions. Skills were repeated until competence was attained. Graduating students have made up greater than 90 per cent of our two hospitals' PGY-1 residents since 1996. Because these residents are responsible for CVLI we are able to obtain performance follow-up in actual clinical settings. We obtained the number of PTXs caused by CVLI for the years 1996 through 2000 as well as for the first 3 months of each academic year (July through September) to determine the impact of our program on this serious complication. The number of PTXs during the first 3 months of 1996-1998 remained stable. After the introduction of our teaching program the number decreased significantly in the years 1999-2000 when compared with 1996-1998 (P = 0.004, t test). The overall yearly decrease for 1999 versus 1996-1998 approached significance (P = 0.06). The introduction of a structured teaching program of CVLI skills appears to have a positive impact in reducing morbidity of PTX. The greatest impact occurs within the first 3 months of the new PGY-1 academic year.