What has been researched and reconstructed, based on archival documents and data from professional literature, is the activity of the State school-polyclinic in Petrinja, from its foundation in 1925 to its termination in 1945. Key figures taking part in its activity have also been highlighted. Founded as one of the first school-polyclinics in Croatia, the State school-polyclinic in Petrinja developed complete preventive and curative health activities aimed at school population in Petrinja as well as at pupils from the village schools in Petrinja County. These activities were based on carrying out thorough check-ups, giving school children vaccination, and taking other counter-epidemic measures, providing health and sanitary education, exercising sanitary supervision of schools and pupils' homes, implementing remedial measures in the field, taking extra care of socially handicapped children, providing regular diet and healthy meals for the poorest (who got prescription glasses for free, as well as medicines, fish-liver oil, who got their teeth filled, hair cut and were given the opportunity to recuperate in the youth holiday camps at the seaside and in the mountains.) The activities also encompassed the efficient treatment of the sick, among whom the various infectious and internist diseases (anaemia, undernourishment, struma, rickets) and dental caries were prevalent. Its twenty-year-old continuous activity aimed at providing school population with health care represents a successful synthesis of preventive and curative health principles based on progressive ideas of social medicine promoted by Andrija Štampar, who was a promoter and reformer of public health service in our regions. Due to being well-organized and the professional enthusiasm of its managers and staff, the State school-polyclinic in Petrinja efficiently promoted public hygiene and addressed the specific health needs of the school population. While promoting integral health care, maintaining and improving physical and mental health of children and youth in the schools in Petrinja and the other schools nearby, it raised the reputation of health care in Petrinja and contributed to the development of the Croatian school of medicine.