The aim of the study was to determine the prevalence and invasion intensity of gastrointestinal parasites in calves from small and middle-sized farms, with a special focus on invasions of chosen protozoa. The analysis included 150 calves from 2 weeks to 5 months of age. The calves came from 30 individual farms with up to 50 cattle managed in a confined system or confined-pasture system. Three types of farms were established: I: up to 20 heads; II: up to 30 heads, and III: up to 50 heads. The feces samples for the analyses were collected directly from the rectum. Each sample was tested using macroscopic and microscopic methods (the McMaster technique, the standard flotation method and the sedimentation method according to Żarnowski and Josztowa). The numbers of oocysts/cysts/eggs per 1 gram of feces (OPG/CPG/EPG) were established. The feces of 94 calves no older than 8 weeks which exhibited traits of diarrhea were analyzed with Bio-X Cryptosporidium parvum Elisa Kit (Kit for antigenic diagnosis of Cryptosporidium parvum by Elisa in bovine feces). The results were subjected to statistical analysis using the Kruskal-Wallis test. The total prevalence of parasites in all groups was 35.33%. The dominating invasion (26%) was with protozoa belonging to Eimeria (most commonly E. bovis, E. zuerni and E. aubernensis). This was followed by Buxtonella sulcata (6.67%), Cryptosporidium parvum (7.45%; Elisa test), Strongyloides papillosus (4.67%) and gastrointestinal nematodes (2.67%). The fewest calves infected with parasites were in Group I, where only the invasions of protozoa were detected. The parasitic infection rates for group II and III were twice and thrice higher, respectively, than for group I. In Groups II and III, nematodes were found apart from protozoa. In all three groups the dominating invasion was Eimeria spp. (Group I: 20%, II: 24%, III: 34%). The prevalence for B. sulcata, S. papillosus, and gastrointestinal nematodes in the groups was as follows: Group I – 2; 0; 0%; Group II – 8; 8; 0%; Group III – 10; 6; 8%, respectively. In the calves aged up to eleven weeks of life, the dominating invasions were Eimeria spp., Cryptosporidium parvum and S. papillosus, while in the calves of 4-5 months of age, B. sulcata and gastrointestinal nematodes prevailed. The average invasion intensities were as follows: Eimeria spp.: 24414 OPG, B. sulcata: 78 CPG, S. papillosus: 86 EPG, and gastrointestinal nematodes: 138 EPG. In the groups, the results were the following: Eimeria spp.: 94,512 (550-414,000); 271 (100-600); 222 (50-500) OPG., B. sulcata 50; 75 (50-100); 70 (50-100) CPG; S. papillosus 0; 75 (50-100); 90 (50-150) and gastrointestinal nematodes: 0; 0; 138 (50-250) EPG. In the calves from all groups, the dominating invasions were caused by parasites belonging to one taxon (genus), they constituted 90%, 80% and 89%, respectively. The statistical analysis did not reveal statistically significant differences between the management system and invasion intensity of Eimeria spp.