HIV infection in children may lead to severe immunodeficiency and life threatening conditions during the first years or even months of life. We report a case of three-moth-old female child with AIDS presenting severe pneumonia, tracheobronchial candidiasis and CMV infection. Child’s mother has not been tested for HIV in pregnancy. Family history and pulmonary insufficiency in the course of pneumonia in the child resulted in performing HIV-screening test. Confirmation of diagnosis led to very quick implementation of antiretroviral treatment. Although the girl survived with good neurological outcome, the presented patient shows missed opportunity for prevention of mother-to-child HIV transmission in Poland.