Background: One of the work patterns which affects the supply of specialists is the phenomenon of dual practice (DP), i.e., working simultaneously in the public and private sectors. Uncontrolled DP in the surgery health workforce can have adverse effects on access to surgeons, efficiency, effectiveness and quality of surgery services. Aims: The aim of this article is to examine the impact of DP on service delivery time by surgeons. Methods: We used a prestructured form to collect data on surgery specialists in all 925 Iranian hospitals. National medical ID codes, council ID codes, first name, surname and father's name were used for data matching. Multilevel linear regression was used to assess the association between DP and study variables, which were recruitment type, faculty status, experience, sex and age. Results: The 4642 surgery specialists in this study, representing 31.08% of the total number of surgeons identified, spent mean 1.09 (standard deviation 0.33) hours full-time equivalent (FTE) on health care service delivery. Specialists with DP had long service delivery time (β = 0.427). Female specialists (β =-0.049) and full-time specialists (β =-0.082) spent less time on health care service delivery. Permanent specialists had higher FTE (P < 0.001) and as the population increases, FTE increases (P < 0.05). Conclusions: Although DP had a direct impact on surgeons' working hours, it seems that a greater share of the difference in working time was used in the private sector services, leading to poor access to surgery services in the public sector. Therefore, it is necessary to develop a systems approach to regulate DP.