Lymphadenopathy is very common in HIV-infected patients (pts). In Portugal tuberculosis (TB) remains the main AIDS defining opportunistic infection and the etiologic diagnosis of enlarged lymph nodes is a challenging problem. The aim of the study was to assess the usefulness of FNAB in the evaluation of these pts. The results of all FNAB exams performed in a 10 year period were analysed. Pts clinical status and demographic, immunologic and virologic data at the time of the procedure were collected. Ziehl-Neelsen stain and culture (Lowenstein and/or Mycobactec), and after the year 1999, PCR for M. tuberculosis (Mt) were performed routinely. Other stainings as well as immunophenotypic and microbiological studies were performed wherever necessary. A total of 524 procedures were performed in 412 pts: in 36% the risk factor for HIV infection was sexual exposure and 61% were IVDUs; 24% pts had AIDS. Pts mean age was 33.5 yrs; 4 pts were children < 13 years old. Adult pts mean CD4 cell count was 330 cells/mm3; 98% of the pts were HIV-1 infected with a mean VL 148490 cps/ml, 18% had undetectable VL and 12% had a VL > 750000 cps/mL. 2% of the pts were HIV-2 infected. Most common FNAB diagnosis was reactive lymphoid hyperplasia n = 287 (55%). TB was diagnosed in 120 (23%) samples based on: acid-fast bacilli in the cytologic smears (n = 51), granulomatous/necrotising caseous patterns (n = 94), Mt positive PCR (n = 44), culture (n = 75). Lymphoma (n = 11). Disseminated MAC disease (n = 5). Other diagnosis (n = 3). In 18% of the samples the material obtained by FNAB was scanty or acellular or non-conclusive - in none of these cases was a malignant tumour later found. FNAB was found to be a simple and reliable evaluating procedure for lymphadenopathies in the HIV-infected patient, enabling the correct diagnosis of a major opportunistic infection.