Radio-telemetry was used to monitor the movements of 18 porcupines (Erethizon dorsatum) in typical west Cascase habitat near Mount St. Helens, Washington. Average linear movement ranged from 249 m in 24 hr to 1,585 m for periods of more than 30 days. The greatest linear movement was 31.1 km in 66 days. Average home range of animals tracked for 10 months or more was 83.5 hectares; the average range of males (106.6 hectares) exceeded that of females (81.2 hectares). Concentration of animals at den sites was not observed. Hunting porcupines with dogs is probably the most effective control measure.