The aim of the study was to monitor the clinical course of T. canis infection in children with particular consideration of the estimation of infected children's immune system. The study comprised 52 children, aged 3 to 18 years, diagnosed and treated at the I Department of Paediatrics and Gastroenterology, Institute Polish Mother Health Centre, in whom infection with Toxocara canis larva was confirmed with serologic test. The control group included 38 children, aged 3 to 16 years in whom no infection with this parasite was detected in serologic test. In the investigated children subjective and physical examinations were performed, clinical symptoms, changes in organs, haematological, biochemical investigations and selected parameters of humoral and cellular immunity were analysed. In children with toxocarosis most frequently not localized abdominal pain, subfebrile body temperature and generalized lymphadenitis were observed. Significantly higher percentage of eosinophil cells and immunoglobulin E serum concentration with decreased percentage of lymphocytes CD3+, CD4+ and CD4/CD8 ratio were found in the investigated children. Toxocarosis diagnosis is difficult because its clinical symptoms are differentiated and not characteristic, what requires broadening of differential diagnosis concerning numerous entities.