Several points can be made from analysis of the published cases of cutaneous mycobacteriosis and those in our series: 1) mycobacterial cutaneous infections are probably more common than is reported-we collected 34 cases over a 10-year period; 2) most patients with cutaneous infections caused by nontuberculous mycobacteria have significant underlying disease; 3) there is a relative lack of classic histologic features in patients with cutaneous mycobacteriosis, and there appear to be diverse forms of clinical presentation; 4) a high index of suspicion is needed in evaluating patients with possible cutaneous mycobacteriosis, and appropriate cultures must be done to establish the diagnosis. In attempting to provide a practical classification of cutaneous mycobacteriosis which includes infection by nontuberculous mycobacteria, we propose the following grouping, which uses simple terms, avoids confusing nomenclature, and incorporates pathophysiologic descriptions and prognostic information: 1) Mycobacteriosis caused by inoculation from an exogenous source. 2) Cutaneous mycobacteriosis caused by spread from an endogenous source. Contiguous spread originates most often with osteomyelitis, but also occurs through autoinoculation of the perirectal, oral, or vaginal skin as organisms are passed or expectorated from pulmonary or genitourinary tuberculosis. 3) Cutaneous mycobacteriosis caused by hematogenous spread. This group includes lupus vulgaris, nodules and abscesses, and acute disease with hemorrhagic pustules. Some mycobacterioses will be difficult to classify when inoculation or hematogenous spread cannot be ruled out. However, the system of classification we have proposed should help clinicians understand and diagnose the diverse forms of cutaneous mycobacterial infections.