This study objectively evaluates recovery of quadriceps and hamstring strength following knee arthroscopy in a group of 43 patients given rehabilitation instructions, but limited supervised rehabilitation. Although the patients did not complain of weakness or functional limitation, isokinetic testing 1, 3, and 8 weeks following surgery revealed persistent weakness in many patients. Incomplete recovery was most apparent when patients were categorized by the degree to which they had recovered normal strength. Results expressed as a mean for the entire group indicated reasonably good recovery and obscured the significant weakness persisting in some patients. Knee extension strength tested at 60 degrees/sec had returned to normal 8 weeks after arthroscopy in only 32% of the subjects. Hamstring strength recovery was better, with 71% having normal strength. Patients may not recognize or report muscular weakness following arthroscopy, yet following 8 weeks of self-supervised rehabilitation many will have objective evidence of persistent weakness. In asymptomatic patients the clinical significance of this weakness is unknown.