Fast pyrolysis of stem wood was performed in a pilot-scale cyclone reactor with a reactor wall temperature of similar to 750 degrees C. Wood powder was introduced to the pyrolyzer at 20 kg/h during the experiments. Stable operation of the pyrolyzer was easily achieved, and the resulting yields of the products were 54.6 wt % of pyrolysis oil, 15.2 wt % of solid residue, and 20.1 wt % of gases. From the ingoing raw material, 3.4 wt % of the mass could be recovered as deposits, mainly on the walls of the reactor and in the oil condensing part of the plant. The mass and energy balance closures were approximately 93% and 89%, respectively. The physicochemical properties of the pyrolysis oil, solid residue, and noncondensable gas were measured and compared to values in the literature. The results also show that it is possible to produce an oil with a very low concentration of ash-forming elements because particle separation has already occurred in the cyclone reactor.