This study was performed to assess the rate of electrode fracture and to provide an account of the occurrences of infection and granuloma associated with percutaneous intramuscular electrodes implanted in upper-limb muscles. Data were reviewed on 858 electrodes implanted in 62 research participants between October 1978 and July 1998. Survival analyses showed that the probability of an electrode remaining intact within the body at 6 months after implantation is 95%, and at 1 year is 91%. The probability of the electrode surviving both the in situ period and extraction after 6 months is 78%, and after 1 year is 57%. Ten participants (16%) experienced at least one occurrence of infection or granuloma associated with in-dwelling electrodes. Five of the twenty-three total adverse medical incidents were associated with electrode fragments retained in the body; the others were associated with intact electrodes. All incidents were localized nonsystematic occurrences and were resolved by administering antibiotics, cleaning the implant site, removing electrodes, cauterizing with silver nitrate, or excising electrodes or granulomas.