In vivo quantification of adipose tissue with magnetic resonance imaging (MRI) was validated with pigs. Thirteen transaxial MRI sections were collected, at intervals proportional to body length, from each pig, which was then killed, frozen, and sliced at the locations of the MRI sections. Adipose-tissue quantities were determined by dissecting each slice, and lipid contents of the dissected slices and of the tissue segments between slices were measured. Compared with dissection, MRI underestimated abdominal percent adipose tissue and overestimated cervical percent adipose tissue by less than 6%. When all 13 sections were used, MRI closely predicted percent lipid and dissected percent adipose tissue with small residual SDs (RSD = 1.9 and 2.1, respectively), which increased only slightly if two sections (4, upper thorax and 8, upper abdomen) were used (RSD = 2.3 and 2.6, respectively). In conclusion MRI accurately quantifies adipose tissue in vivo, matching values produced by dissection and chemical analysis.