BACKGROUND: The prevalence and time trends of food allergy change during childhood depending on the age of the child and the type of food. OBJECTIVE: To study prevalence and longitudinal trends in food allergy from birth to 18 years in an unselected birth cohort in the Isle of Wight. METHOD: Information on food allergy was collected at ages 1, 2, 4, 10 and 18 years from the Isle of Wight Birth Cohort (n = 1456). Skin prick testing (SPT) was performed at the age of 1 and 2 years in symptomatic children. At 4, 10 and 18 years of age, participants were tested to a panel of food and aero-allergens. Food allergy was diagnosed based on the criteria: symptoms suggestive of a typical IgE mediated reaction and reaction <4 hours following exposure to a known food allergen. McNemar's test was used to determine significance of changes in prevalence over time. RESULTS: The prevalence of food allergy remained relatively constant in early childhood (5.3%, 4.4% and 5.0% at 1, 2 and 4 years respectively), with significant decline at 10 years (2.3%, p<0.001 versus 4 years) followed by significant rise at 18 years (4%, p=0.02 versus 10 years). Cow's milk (1.6-3.5%) and egg (1.1-1.4%) were the most common allergens in the first 10 years with peanut (1%) and tree-nuts (0.5%) becoming more prevalent beyond 10 years. Fruit and wheat allergy were less common at 10 years, and shellfish and kiwi emerged during adolescence. The prevalence of food allergy plus positive SPT were 1.3%, 0.8%, 0.8%, 0.9% and 2.2% at 1, 2, 4, 10 and 18 years respectively. CONCLUSION: Food allergy is highly prevalent in infancy with partial resolution during late childhood. However, a number of children acquire new food allergy during adolescence resulting in a relatively higher prevalence at 18 years.