Objectives: Domestic violence has a long history in human life and is the most prevalent form of violence against women. It is a worldwide problem that occurs in all societies with different cultures and socioeconomic groups. As this type of violence occurs generally inside families, children may be more prone to be directly exposed to this type of violence and the aftermaths compared to other types. Exposure to domestic violence has serious and long-lasting effects on emotional and cognitive conditions of children and also on their attitudes towards violence as a method for conflict management. This study has done by the purpose of assessment of frequency and nature of Tehran’s secondary school student’s exposure to their parent’s physical violence against each other. Method: It was a questionnaire survey on senior secondary school population in Tehran, in educational year 2005-06. The sampling method followed a multistage cluster sampling based on the exhaustive list of all senior secondary schools in 19 districts of Tehran and included all high schools, vocational training schools, technical training schools, and mixed vocational-theory (Kaar-Daanesh) schools. The frames were separated for girls and boys. Each district was considered as a stratum and the weight for each stratum in the sample was proportional to the population of the district. Findings: There were 1495 students participating in this survey, where the prevalence was estimated to be 22.8% (18.9% - 26.8%) more than half of them had eye-witnessed it (59.8% 95% CI: 49.6% - 70.0%). It is twice more prevalent in girls than in boys (31.2% vs. 16.1%). Recent exposure to this type of violence was much less prevalent (5.7% 95% CI: 3.6% - 7.8%) in the last month. The main type of violence was hand beating alone (57.1% 95% CI: 46.8% - 67.3%) and there was mainly fathers who had perpetrated the violent act (54.3% only fathers vs. 3.4% only mothers). The exposure was long lasting and in those with more than one exposure the mean duration was 5.1 years (4.4-5.8). Results: Exposure to physical violence between parents is a common problem among teenagers in Tehran, a considerable portion of them had eye-witnessed it. It is of a continuous nature starting from childhood and lasting to mid teenages. Based on the results of this study, children are highly exposed to violent behavior between their parents and these events are often continuous. There is an urgent need to explore this possible source of future violence and the short and long term consequences of those exposures. Also, there is a need to conduct more analytical studies on the risk and protective factors for this problem, as well as occurrence of domestic violence per se.