In 1990, a random sample of 567 persons of the 15-69-year-old population living in the Western part of Copenhagen County, Denmark, was patch tested in a cross-sectional study. In 1998, a follow-up study was performed. Out of 540 invited, 365 (68%) were re-patch tested. In the follow-up study, the persistence of allergic contact sensitivity, defined as 1 or more positive patch tests in both surveys, was 71% (37 out of 52 subjects). Nickel allergy persisted in 79% (19 out of 24 subjects), while 60% (21 out of 35 subjects) had a positive patch test reaction to 1 or more allergens, other than nickel, in both surveys. The lowest persistence was 50% (5 out of 10 subjects) and this was found for patch test reactivity to 1 or more of the cosmetic ingredients included in the patch test series. 8 years after the baseline study had demonstrated allergic contact sensitivity, 71% of the subjects still had at least 1 positive patch test. Nickel allergy persisted in 79%. Allergen avoidance should probably be lifelong to prevent elicitation of contact dermatitis.