Hand eczema in a population-based twin cohort of 6666 persons aged 20-44 years was investigated by means of a questionnaire regarding skin symptoms on the hands and self- or physician-diagnosed hand eczema. Genetic influence was observed by significant differences between identical and fraternal twins regarding casewise concordance rate and correlations in liability under the threshold model. The casewise concordance rates were almost twice as high in identical compared with fraternal twins in both sexes. By extension of the threshold model a joint analysis could be performed, resulting in a heritability estimate of 0.65. Tendencies towards stronger genetic influence for men and for younger individuals were present, but neither was statistically significant. No particular symptom pattern expressed especially strong or weak genetic influence. Hereditary factors for hand eczema were observed despite a presumably substantial individual-specific environmental variation. The hypothesis that hereditary risk factors may play a significant part in the development of hand eczema in the general population, when no extreme environmental exposure exists, seems justifiable. The relevance of known individual risk factors such as atopic dermatitis or contact allergy in relation to heredity remains to be analysed. The possible importance of age and temporal change also needs further consideration.