Accurate prediction of the droplet size distribution in steam turbines is crucial for the correct analysis of wetness losses and other two-phase effects. Measurements taken in the later stages of LP turbines have shown broader size distributions with larger average sizes than those predicted by numerical methods. One hypothesis is that the broad distributions stem from the unsteady interaction between blade rows. Wake segmentation in successive rows means that fluid particles passing through the machine have different dissipation histories which in turn causes a wider range of nucleation and droplet growth rates. A method for calculating unsteady, viscous, condensing flows in multi-stage steam turbines is described. This is based on an established single-phase flow solver with nucleation and droplet growth incorporated via moment evolution equations for the poly-dispersed liquid phase. The method can be used to compute two- and three-dimensional steady and unsteady flows, time accuracy being preserved for unsteady calculations by means of the dual time-stepping technique. Comparison between computed results and experimental data is presented for nozzle and cascade flows for the purpose of validation. Preliminary multi-stage calculations have been performed on a thin-slice three-dimensional geometry of a two-stage turbine. These highlight some of the features of wake chopping and indicate that fluctuating nucleation zones may contribute to a broader time-averaged size distribution. However, they also show that the effects of wake chopping may be smaller than the effects of variation across the passage, especially if the nucleation zone interacts with the trailing edge shockwave so that condensation is delayed for part of the passage. The method is then applied to a five-stage model turbine. One-tenth of the annulus of the turbine is modelled and an integer blade number ratio between rows is achieved by scaling the blade profiles, keeping the pitch-chord ratio and stagger angle constant. The results are compared with pressure measurements and droplet Sauter mean radii obtained from experimental optical data. The predicted droplet sizes agreed with the measurement data to within ±50 % of the measured value but showed discrepancies in the detailed stream-wise and span-wise trends. Calculations of this type are at an early stage of development and improvements in mesh quality and boundary and interface treatments will be required before firm conclusions can be drawn.