BACKGROUND: The surface area of scars is an important outcome parameter in scar assessment. It is often used to quantify the extent of scar features, such as pigmentation disturbances, hypertrophy, and contracture. Currently available techniques for measuring the surface area are known to be cumbersome or do not meet the basic clinimetric criteria (i.e., reliability and validity). Three-dimensional stereophotogrammetry is a technique that may improve the quality of surface area measurements. The aim of this study was to investigate the reliability and validity of three-dimensional stereophotogrammetry for measuring scar surface area. METHODS: In a cross-sectional study, two independent clinicians photographed and measured 50 scar areas of 32 patients using a handheld stereographic camera, to assess reliability. Subsequently, using planimetry, the scar surface was traced on a transparent sheet (considered the accepted standard) to assess validity. RESULTS: Three-dimensional stereophotogrammetry showed good reliability, with an intraclass correlation coefficient of 0.99 and a coefficient of variation of 6.8 percent. To visualize the differences between the two observers, data were plotted and the limits of agreement were calculated at 0 ± 0.19 × mean surface area. Also, excellent validity was found, with a concordance correlation coefficient of 0.99. CONCLUSION: This study showed that three-dimensional stereophotogrammetry is a reliable and valid tool for research purposes in the field of scar surface area measurements. Copyright © 2013 by the American Society of Plastic Surgeons.