Mesenteric adipose tissue, located in the mesenterium of the intestines, is believed to play a central role in the development of obesity-related diseases. We have found that mesenteric fat samples harvested from rodents are frequently of poor quality, exhibiting partly degraded RNA. To investigate the background for this observation, we screened adipose tissue samples from two independent studies on rodents for markers of different tissues and cell types. We found that mesenteric adipose tissue samples of low quality are "contaminated" by pancreatic tissue. To locate the affected area, we dissected the mesenteric fat depots from 14 mice and measured abundance of pancreas-specific gene expression and amylase activity. As expected, we observed that the proximal section of the mesenterium, located near the pancreas, expressed pancreatic markers, whereas the distal sections did not. Approximately one-third of the mesenteric adipose tissue depots contained pancreatic tissue. Because the boundary between pancreas and mesenteric fat cannot be easily distinguished during dissection, we conclude that investigators should routinely exclude the proximal section of the mesenteric adipose tissue depot to avoid pancreatic contamination.