During a 9-month period at a small surgical center, seven cases of postarthroscopic septic arthritis occurred after 352 arthroscopic procedures, for an infection rate of 2.0%. Electrocardiographic cables contaminated with Pseudomonas aeruginosa from an unsterile cleaning solution probably led to two shoulder infections. Five other infections (one definite Staphylococcus aureus and three definite and one possible coagulase-negative staphylococci) were attributed to inadequate arthroscope disinfection. In the initial phase of the outbreak, use of intraoperative intraarticular corticosteroids correlated with the occurrence of infection.