As part of a larger retrospective study examining all knee injuries sustained by the University of Iowa wrestling team over 6 years, prepatellar bursitis was found to be the most frequent injury and, therefore, was examined in depth. Of the 136 wrestlers studied, 13 developed an initial case of prepatellar bursitis. This represented 21% of all initial episodes of knee injuries. Five of these wrestlers had no recurrences, but the other eight together had 20 recurrences. Median time lost for the initial injury was only 4 days, but recurrences and surgeries added significantly to the total time lost. There were only two cases of septic prepatellar bursitis, but there have been six cases (in four wrestlers) in the three seasons since the end of the larger study period. The infecting organism in all but one case was Staphylococcus aureus and was penicillin-resistant in all but one. There was no clinical evidence of infection in 50% of the cases, emphasizing the need to do a Gram's stain and culture (and, therefore, an aspiration) on all cases of prepatellar bursitis. The prognosis appeared better if the wrestler had no previous history of bursitis, suggesting that pathologic changes in the bursal wall may impair its defense mechanisms. In sharp contrast to all other knee injuries, most prepatellar bursitis cases occurred in the off-season. Most developed insidiously, but direct impact during a takedown maneuver is suspected as being the most frequent cause.(ABSTRACT TRUNCATED AT 250 WORDS)