Cormorants are desirable subjects for food web studies using stable isotopes (C and N) because of global fisheries conflicts, but no validated lipid-normalization procedures are currently available for any cormorant species. Accordingly, the effects of chloroform-methanol and petroleum-ether lipid extractions and three published lipid-normalization models on stable C and N isotope signatures in Double-crested Cormorant (Phalacrocorax auritus) muscle and liver tissues were investigated. The presence of lipids in cormorant muscle and liver decreased δ¹³C values by approximately 1–2‰, more so than has been reported in other birds. Cormorants showed large variation in the relationship between the C:N ratio of bulk tissue and the change in δ¹³C values after lipid extraction, violating a major assumption of published lipid-normalization models. Despite this violation, two of the three tested models performed reasonably well for correcting δ¹³C values. The circumstances under which these models might fail are unknown, so caution is warranted when applying them to new species. Petroleum-ether lipid extractions did not reduce the C:N ratio of tissue samples to those of pure proteins (4.0 or below; over half of the samples ranged from 4.38 to 5.27); thus, lipid extraction using chloroform-methanol is recommended to ensure the greatest accuracy of carbon isotope analyses of cormorant tissues.