Many important questions in ecology and conservation biology require assessment of the body condition of animals, which is often achieved using mass and length data. However, fully quantitative condition indices can be difficult to obtain in the field for large taxa like marine turtles. Therefore, rapid visual-assessment techniques for categorizing condition can be useful for field studies. Here, we test whether a visual method of categorizing body condition in the Green Turtle (Chelonia mydas) based on the shape of a turtle's plastron is comparable to two commonly used body condition indices derived from mass and length measurements. Condition scores for both mass–length indices varied in the expected manner with our visual condition categories, verifying that the rapid visual assessment technique accurately reflects differences in body condition. This technique should aid many field studies of turtles where body condition data are required but mass data cannot easily be obtained.