Models for predicting the biomass of forest trees are becoming increasingly important for assessing forest resources and carbon sequestration in forests. We developed functions for predicting the biomass and basic density of above- and below-ground parts of Norway spruce (Picea abies (L.) Karst.) in Denmark. Separate models were developed for branches (including foliage), stem and the below-ground stump and root system as well as for the aggregate components of total above-ground biomass and total tree biomass. Trees were sampled in 14 forest stands, reflecting the range of growth conditions and thinning practises of Norway spruce in Denmark. Because of inclusion of experimental plots, data reflected a wider range of thinning practices than commonly used in forestry practice. The data included measurements of biomass and basic density from 114 trees, two of which were regarded as outliers and consequently excluded in the final model estimation. The final models reflected known properties of tree growth and allocation of biomass among different tree components of even-aged Norway spruce. The models were successful in predicting biomass, basic density and biomass expansion factors across a wide variety of tree sizes, stand treatments and growth conditions. The models are believed to substantially improve national estimates of carbon sequestration and biomass resources.