Evidence suggests that high-quality diets enriched with essential fatty acids (EFA) and other nutrients can ameliorate canine atopic dermatitis (AD). This study compared such a diet (Eukanuba Veterinary Diets Dermatosis FP) with a home-cooked equivalent (fish and potato) in a randomised, single-blinded, cross-over trial. Twenty dogs with perennial AD were randomly assigned to receive either the test (group A) or the control diet (group B) for 1 month, followed by the contrasting diet for a further month. Canine Atopic Dermatitis Extent and Severity Index (CADESI version 2) and pruritus (visual analogue scale) scores were recorded at days 0, 30 and 60. Eight dogs in each group completed the study. CADESI scores significantly declined when dogs were fed the test diet (group A P < 0.01; group B P < 0.001), and increased (group A P < 0.05) or remained steady (group B) on the control diet. CADESI scores decreased in 15 of 16 dogs fed the test diet, but this was less than 50% in all cases. Pruritus scores also declined when dogs were fed the test diet compared to the control diet, but this was only significant for group A (P = 0.027). Pruritus was reduced in 11 of 16 dogs fed the test diet, but this was 50% or more in only two dogs. This trial provides evidence for the efficacy of Eukanuba Veterinary Diets Dermatosis FP in canine AD, although it is likely that most cases will require adjunct therapy. The mechanism is unclear, but may involve increased and balanced EFA levels.