The farming of deer is now widespread throughout Argentina and Paratuberculosis has been identified in red deer (Cervus elaphus) in a herd in the Province of Buenos Aires. In this study we examined three hundred and thirty two animals of different ages (8 to 84 months), selected at random and divided into seven groups, 50 % females and 50 % males each. Another eight seropositive animals were selected because they had clinical signs of Paratuberculosis. Blood for indirect absorbed ELISAs (ELISA 1: bovine anti-IgG, and ELISA 2: deer anti-IgG), Immunodiffusion test (AID) were collected. Feces and tissues for isolation of Mycobacterium avium subsp. paratuberculosis (Map) were cultured on Herrold's with and without mycobactin. Results showed that the ELISA 2 test detected a significantly higher percentage of reactor animals than AID. There were no differences in the percentage when the ELISA 1 test was compared with AID and the ELISA 1 with ELISA 2. In turn, ELISA 1 detected a higher percentage in the stratum of 12 and 84 months of age. Analyzing the three tests, it was proved that the highest incidence of seropositive animals occurred in the group of 84 month old males. The absorbency values of both ELISAs were highly correlated (r=0.865). The ELISA 1 test had a sensitivity of 83.3% and the AID test turned out to have a sensitivity of 33%. Twelve strains of Map were isolated. In the mesenteric lymph nodes of the animals with Paratuberculosis there was moderate to severe infiltration with macrophages (MO) and Langhans' giant cells (LC). The kind of lesion observed was similar to the IIIb and IIIc types established for small ruminants. All ZN smears were positive for MO and LC lymph nodes and intestine sections were positive to immunohistochemistry, showing the higthlest specificity to Map inside MO and LC.