In Iceland and on the Faroes the carabid Nebria gyllenhali Schn. is dimorphic for legcolour; effectively all samples contained both red- and black-legged individuals. In Iceland (18 sites: 1-100 % red) the frequency of red-legged was lowest in the southern and highest in the northern and western parts. The frequencies at adjoining sites were positively autocorrelated (p ≅ 0.01) and a stepwise multiple regression analysis yielded a strong, negative correlation between the frequency of red-legged and temperature/precipitation variables (R2 = 0.994). On the Faroes (50 sites: 20-100 % red) the highest frequencies of red-legged occurred in the south but the geographic pattern was less distinct than in Iceland and the positive autocorrelation was weaker (p 0.05). Due to lack of detailed meteorological records the negative correlation between the frequency of red-legged and temperature/precipitation could only be inferred from general information and topography. The correlations between frequency of leg-colour form and climatic variables may be casual but different other possible reasons for the observed geographic distribution patterns are discussed. Naturally no definite answer can be given on the basis of the entirely observational data. A genetic basis for the leg-colour dimorphism is assumed, but cross-breeding experiments are required.