OBJECTIVE To review records of 166 patients who underwent treatment for Mycobacterium marinum tenosynovitis of the hand and wrist to identify factors associated with functional outcome. METHODS Records of 97 men and 69 women aged 13 to 85 (mean, 50) years who underwent treatment for suspected M marinum tenosynovitis of the hand and wrist were retrospectively reviewed. All underwent open biopsy; synovectomy was performed when florid synovitis was present. Rifampicin and ethambutol were usually prescribed. Clarithromycin, minocycline and/or levofloxacin were used as adjuvants if there was drug intolerance, allergy, or relapse. The duration of antibiotic treatment depended on the clinical recovery. Patients were followed up for one year after completion of drug treatment. Functional outcome was considered excellent for those with >195º total active motion (TAM) and >75% return of motion, good for those with 130º to 195º TAM and 50 to 75% return of motion, fair for those with 65º to 129º TAM and 25 to 49% return of motion, and poor for those with<65º TAM and <25% return of motion. RESULTS The mean delay in presentation was 4.9 (0.3-120) months. 93 of the patients presented with disabilities (flexion deformity or reduced range of motion), 64 of whom presented one month after injury. 37 (22%) of the patients had received intralesional steroids prior to admission, 30 of whom presented one month after injury. 32 (19%) patients were treated with antibiotics alone, whereas 134 (81%) patients underwent debridement in addition to antibiotic treatment. The mean duration of antibiotic treatment was 7.2 (range, 0-29) months. Of the 156 patients who completed the follow-up, functional outcome was satisfactory in 128 (82%) and unsatisfactory in 28 (17%). Steroid injections and late presentation led to worse functional outcome. Patients with unsatisfactory outcome were more likely to have received intralesional steroid injections (43% [16/37] vs. 10% [12/118], p<0.001, Pearson Chi squared test), have presented >2 months after injury (27% [21/79] vs. 9% [7/77], p=0.004, Pearson Chi squared test), and have undergone synovectomy (23% [28/124]) vs. 0% [0/32], p=0.001, Fisher's exact test). Worse functional outcome correlated with late presentation (r=0.218) and the greater number of debridement procedures (r=0.453). CONCLUSIONS Delayed antibiotic treatment of M marinum infections and steroid injections were associated with unsatisfactory outcome. Clinicians must have a high index of suspicion for this condition and avoid inappropriate management such as intralesional steroid injections. Public awareness to this condition should be raised.