Tuberculosis is reappearing, due to diminished surveillance, illegal immigration, the HIV epidemic and certainly also due to emerging resistance. The clinical expression of cutaneous tuberculosis depends on the stage of development, the clinical background and the virulence of the germ. Diagnosis is predominantly clinical, but laboratory results also play a role. Treatment involves the quadruple antibiotic treatment prescribed for any tubercular infection. Atypical mycobacteria are widespread throughout the environment and are pathogenic, but also saprophytic, comensal and opportunistic, figure a favourable setting in the immunodeficient individual. Following entry by penetrance, the early lesion is papulonodulary, nodulary, keratoid, crusted, ulcerated, sporotrichoid, generally without peripheral adenopathy. Histological examination discloses a granulomatous reaction limiting the development of the infection; such development is absent in the immunodeficient patient, thus explaining the spread. The most common mycobacterial infection in France, generally in the immunocompetent individual, is "aquarium disease" which follows a benign course; the most common in tropical areas is Mycobacterium ulcerans; whereas Mycobacterium avium intracellulare, fortuitum and chelonae cause, in the immunodeficient patient, severe and extensive infection. Treatment should start as soon as diagnosis is made and the germ identified.