Timber prices belong to the most important variables affecting the optimality of forest management. On the other hand, forecasting of timber prices is very uncertain. One difficulty when using past time series data in forecasting future timber price development is the possibility of changes in the markets and in the society at large. Expert knowledge can be applied in forecasting of timber prices as information additional to that provided by time series modelling. This paper presents an approach utilising both time series data and expert judgments in modelling future timber prices. A time series model is used as the basis for the approach. Parameters describing future timber price trends, variation in future timber prices, and the probabilities of price peaks taking place in the future are estimated with expert judgments as the basis. A case study involving 12 experts was carried out in Finland, and models were estimated for all the six major timber assortments in the country. The model produced can be utilised in the optimisation calculations of forest planning.