Gross growth efficiency of Lake Geneva brown trout (Salmo trutta ) was estimated by monitoring age-related PCB and p,p'-DDE accumulation, food contamination and annual growth. Estimation was carried out using 3-, 4-, and 5-yr old fish. Roach (Rutilus rutilus ) were determined as the main component of trout diet. Estimated growth efficiency coefficients were 0.4 (3-4 yr old fish) and 0.17 (4-5 yr old fish). Nevertheless numerous parameters can affect the result; their respective influences are discussed. Related to fish age, PCB and p,p'-DDE concentrations increase if expressed on a wet weight basis, but not if expressed on a lipid weight basis.