Background The role of family physicians (FPs) in the metropolitan area is critical in identifying risk factors for diseaseprevention/controland health promotioninvarious age groups. Understanding people's preferences and interests in choosing a FP can be an effective and fundamental step in the success of this program. In this study factors affecting the FP selection by Iranian people referred to health centersin the most populous areas in the south of Tehran were assessed and ranked.Methods Asequential mixed-method (qualitative-quantitative) triangulation approach was designed with three subject groups of people, physicians, and health officials.The Framework method was used to analyze interviews transcribed verbatim. After implementing an iterative thematic process, a 26-item quantitative questionnaire with high validity and reliability was draftedto evaluatethe different factors.A convenient sampling method was usedto select 400 subjectson a population-based scale to quantitatively rank the most critical selection factors.Results The selection factors were divided into six centralized codes, including FPs' ethics,individual, professional and performance factors;patients underlying disease and individual health, and disease-related factors;clinic-office’s location and management factors;democracyfactors;economic factors; andsocial factors. After filling out the questionnaires,the most important factors in selecting FP were aspecialistdegree in family medicine (FM), performing accurate examinations, taking correct biography, and spending enough time to visit by the doctor, respectively. However, the parameters such as being a fellow-citizen, being same gender, and physician's appearance were of the least importance.Conclusion There is a necessity to expand the new medical specialty in FM because it was considered as the first people's priority. The clinical andadministrative healthcare systems should schedule the entire implementation process to oversee the doctor's professional commitment and setting the visit times of FP.