Fifteen cancer patients have developed catheter-related infections caused by the Mycobacterium fortuitum complex (M. fortuitum and Mycobacterium chelonae) at M. D. Anderson Cancer Center since 1978. Eleven patients had bacteremia and four had catheter site infections. Nine infections were caused by M. fortuitum and six by M. chelonae. All four bacteremic patients whose catheters were initially removed and who were treated with antibiotics recovered, whereas for all of the seven bacteremic patients whose catheters remained in place, the infection relapsed or treatment failed. Six (86%) of the latter group ultimately responded to additional antibiotic therapy when the catheter was removed. Successful treatment of local catheter infections was accomplished by catheter removal alone or in combination with antibiotic therapy. Fourteen additional cases have been reported, and eight (57%) of these patients also had underlying cancer. Patients with septicemia or an infection at the catheter insertion site responded to catheter removal and appropriate antibiotics. Patients with infection in the catheter tunnel (tunnel infection) responded only after surgical excision of the tissue surrounding the infected tunnel. M. fortuitum complex is a cause of catheter-related bacteremia in patients with cancer. Appropriate treatment consists of antibiotic therapy and catheter removal. Tunnel infections usually also require surgical excision.