The aim of this work was the evaluation of fatty acids contents in meat and selected offal in lambs fed a diet containing silage of whole plants of genetically modified maize (Bt) MON 810 line. The material consisted of 14 Polish Merino lambs of mean start body weight 24 kg. There were two feeding groups selected of 7 lambs each. In the control group (K) the lambs were fed isogenic maize silage, which in the second group (GMO) was substituted with the modified maize silage (Bt) MON 810 line. After 70 days of feeding (feed portions were standardised according to the DLG system) the lambs were slaughtered and dissected. The results were evaluated statistically and the significance of differences was calculated with the two factor variation analysis (nutrition, tissue). Feeding genetically modified maize silage did not change, in a statistically significant way, the contents of any main fatty acids in the pool of all acids nor the contents of the totals and their proportions, while the factor causing clear differences was the tissue. Differences for the majority of the results were statistically significant. Statistically significant interactions noted (nutrition x tissue) are probably due to different values of these traits in the analysed tissues.