Background: Informal payments are out-of-pocket payments that are paid to health care providers for services that must be provided to patients with no cost. These services can be in various forms including cash or non-cash contributions and presents. Since the informal payments have a significant effect on the health care system in terms of equity, access, and efficiency, the aim of this study was to estimate the amount and frequency of informal payments in patients referring to the Isfahan hospitals. Methods: This study was a cross-sectional study which was carried out during the last six months of 2015 in 10 hospitals of Isfahan. 250 patients were randomly selected and their demographic profile consisted of gender, age, type of insurance, payment amount, type of treatment, hospital, etc. To collect the data regarding the amount of informal payment obtained by health care providers, questionnaires and telephone interviews were adopted and data analysis was carried out using SPSS 19 software. Results: Results of the study showed that 27. 2 % of patients had informal payments. The average informal payment made to doctors was 590, 000 Tomans, to nurses was 23, 500 Tomans and to other staff was 14, 500 Tomans per patient. With informal payments compared to non-informal payments, the results revealed there was significant statistical differences (P<0. 05)between breadwinner’ s job and education, his/her approximate monthly expenditure, patient’ s hospital ward, length of stay, and type of treatment and hospital. Conclusion: This study revealed the amount, frequency and variables that contributed to patients’ informal payments. Considering the negative consequences of informal payments, it is recommended that by controlling and studying the influential variables as well as paying enough attention to the amount of these payments in different groups, these payments can be detected and prevented.