Seventy-four dogs from the State of Rio de Janeiro with ulcerated cutaneous lesions were submitted to clinical, dermatological,parasitological, mycological, histopathological and cytopathological exams, a leishmanin skin test, an indirect immunofluorescence(IIF) test for leishmaniosis, and nonspecific laboratory tests such as blood count and serum biochemistry.Sporothrix schenckiiwasisolated from 41 dogs andLeishmania(Viannia)braziliensiswas isolated from 33 animals. Most dogs with sporotrichosis were fromthe municipality of Rio de Janeiro (53.7%) and presented ulcerated cutaneous lesions on the head (68.3%). Laboratory alterations inthese animals included anemia (58.5%), hypoalbuminemia (83%) and hyperglobulinemia (75.6%). Histopathology revealed thepredominance of a chronic granulomatous inflammatory infiltrate (70.7%), and yeast-like structures were detected in 17% of thehistopathological exams and in 32% of the cytological exams. Three of 41 dogs with sporotrichosis were seropositive by IIF forleishmaniosis and 2 of 20 animals tested within this group had a positive leishmanin skin test. Similarly, most of the 33 dogs withleishmaniosis were from the municipality of Rio de Janeiro (69.7%) and had ulcerated cutaneous lesions on the head (84.8%).Laboratory alterations in these animals included anemia (66.7%), hypoalbuminemia (100%) and hyperglobulinemia (91%).Histopathology showed the predominance of a chronic granulomatous inflammatory infiltrate (63.6%) and amastigote forms weredetected in 30.3% of the histopathological exams and in 31.8% of the 22 cytological exams performed. About 72.7% of the dogswere seropositive by IIF and five of seven animals had a positive skin test. Due to the clinical similarities, histopathological andnonspecific laboratory results similarities, the serological and skin tests for leishmaniosis positive in dogs with sporotrichosis, andthe overlapping endemic areas in Rio de Janeiro, the differential diagnosis between the two diseases requires the demonstration oftheir respective etiological agents.