The Hydrological Simulation Program - FORTRAN (HSPF) in its personal computer version, release 10.10, was used to perform the hydrological simulation of a sub-watershed of the Occoquan River drainage basin. The sub-watershed selected was the Cub Run Watershed located in the northern area of the Occoquan River catchment. A model in the form of a User Control Input (UCI) file was prepared. The Cub Run Watershed was analyzed considering its geological, edaphic and weather characteristics, and segmented accordingly. The model was calibrated to adjust simulated results to observed data. Several calibration runs were executed and a final run was done considering a further segmented watershed. The simulation results were good even when not all the desired data could be found. The annual percent difference between the best calibration run and the observed results was 21.28%. The ten-month percent difference, excluding June and July, was 5.82 %. The first value is a fair result for hydrologic calibration, the second value is an excellent result for the same type of calibration. Additional segmentation did not further improve the results obtained during the best calibration run. Differences in the calibration when considering just a pervious segment or two segments (one pervious and one impervious) could be noted, indicating the importance of considering impervious surfaces for the simulation. HSPF reacted quite logically to variations in the calibration parameters and the results from those variations could be predicted beforehand. In summary, the PC version of HSPF was demonstrated to be a good management tool for the hydrological simulation of this watershed.