The article analyzes publications dealing with the problem of mycobacteriosis, which show that in 95% of cases its cause in HIVpositive individuals are bacteria referring to M. avium complex (MAC) that cause disease-MAC infection with a high (up to 50%) lethality level. Early adminiatration of adequate therapy might improve the prognosis for this cohort of patients. But similarity of clinical-radial signs of MAC infection and other secondary diseases require fast and reliable methods of etiological diagnosis of mycobacteriosis. The most characteristic clinical-radial and laboratory markers of MAC infection in HIV-infected individuals are as follows: B symptoms, namely, weight loss, fever, weakness, abdominal pains, diarrhoea; mesenteric lymphadenopathy in combination with or without intrathoracic lymphadenopathy; profound immunodeficiency (number of CD4+-lymphocytes below 50 cell/μ l); anaemia, haemoglobin levels below 90 g/l in combination with or without cytopenia. Laboratory diagnostics of mycobacterioses is progressively developing: automated analyzers with liquid nutrient media are extensively used; rapid immunochromatographic tests enabling fast differentiation of tuberculosis from non-tuberculosis mycobacteria have become available; reagent kits allowing differentiation of the most common NTM have been introduced. Also, differentiation of NTM by the sequencing technology considered as the "gold standard" is possible. But so far, only cultures can serve as identification material, which increases the time of making a diagnosis. Along with fast determination of a causative agent, detection of MAC sensitivity to antimicrobial drugs also presents a serious difficulty, which also tells on the effectiveness of therapy.