||Diameter increment in Norway spruce (Picea abies) forests in Southern Norway was investigated in relation to exceedance of critical loads (MAGIC), climate (average temperature in April), precipitation deficit (in relation to normal 1961-90), site productivity, stand density, tree age and cutting class. The frequency and spatial distribution of plots with relatively low increment in relation to exceedance of critical loads were analysed. All forest data were divided into 48 strata based on average temperature in April, cutting class and site productivity. Potential geographic clustering of sites with exceedance of critical loads was investigated by means of block-size ANOVA. We applied a bonferroni z-statistic test to determine if the forest located in clusters with exceedance of critical loads had relatively lower increment in relation to expected from climate, site productivity and cutting class, A cluster with exceedance of critical loads was found in South-Eastern Norway. Within this area, increment was significantly lower than suggested by April temperature, site productivity and cutting class. The lower increment could not be explained by differences in tree age, stand density, precipitation deficit, or distribution of vegetation types. The majority of the plots with critical load exceedance occurred in areas with a relatively long growing season, but also the highest pollution loadings. Within this area, the frequency of plots with relatively low increment was positively correlated to exceedance of critical loads. Forest with relatively low increment also had a significantly lower crown density. The exchangeable Ca and Mg contents in the humic layer, as well as base saturation, was significantly lower in areas with exceedance of critical loads. We conclude, that there is a geographic and spatial consistency between exceedance of critical loads, relatively low increment and relatively high defoliation in areas of South-Eastern Norway. The areas with reduced forest vitality correspond with areas where fish-die back, soil and water acidification has been documented.