A cross-sectional study was conducted to investigate the influence of the co-payment policy in a community setting on the purchase of prescription medications for children with acute infections. Data for all purchased medications prescribed for children with an acute infectious disease were gathered from a pediatric health care center over a 6-week period. Parents of the sick children and controls were interviewed by telephone, using a short sociodemographic questionnaire, and were asked to state their reasons for not purchasing (either partially or completely) necessary medications, primarily antibiotics. Of the 779 children who received a prescription for antibiotics during the 6-week period, 162 (20.7%) failed to take the complete course of antibiotic treatment. One hundred and one parents of these children (62.3%) were interviewed, of whom 30 (29.7%) claimed that the main reason for not buying the full course of antibiotic medication was the cost. This group is characterized by low income, overcrowded housing conditions and a large quantity of prescription medications. The cost of prescribed medication under the co-payment policy is a serious barrier to the purchase of prescribed medication for children with acute infections in the primary care setting. The policy has a particularly deleterious effect in under-privileged populations and is in contradiction with the proclaimed principles of justice and equality underlying the obligatory Israeli National Israeli Health Insurance Law and similar laws in other western countries.