Stretchmarks are fine lines (rashes) found in the abdomen, breasts, buttocks, and upper arms or thighs of pregnant women. The American Academy of Dermatology states that stretchmarks about 90% of pregnant women experience hyperpigmentation. In Korea, a survey of pregnant women in several cities showed an incidence of stretchmarks of 18-20%. In Indonesia 2397 patients in 1998-2005, as many as 21% 7 or 297 people experienced stretchmarks. In North Sumatra 27.4% suffered stretchmarks in pregnant women in trimesters II and III. This study aims to determine the knowledge of pregnant women about stretchmarks during pregnancy at the Obgyn Poly Hajj Hospital in Medan in 2011. This study uses a descriptive design that is using primary data obtained directly from respondents using a questionnaire. The population in this study were all pregnant women who came to check their contents to the Poly Obgyn Hajj Hospital in Medan in August 2011 using accidental sampling technique. Data processing through the process of editing, coding, tabulating, scoring, and analyzing data. Based on the research results of knowledge of pregnant women about stretchmarks during pregnancy the majority of respondents were knowledgeable enough as many as 12 people (48%), well-knowledgeed as many as 9 people (36%), as poor as 4 people (16%). Based on the results of this study it can be concluded that the knowledge of pregnant women about stretch marks during pregnancy is considered sufficient. The results of this research are expected to be useful as an increase in knowledge for pregnant women who have a pregnancy check up at the Polyclin Obgyn Medan Hajj Hospital in 2011.