Whether telecommuting and personal travel are complements or substitutes is a key question in urban policy analysis. Urban planners and policy makers have been proposing telecommuting as part of travel demand management (TDM) programs to reduce congestion. Based on small samples, several empirical studies have found that telecommuting has a substitution effect (although small) on commute travel, and have thus argued that policies promoting telecommuting might be promising in reducing travel. Using data from the 2001 and 2009 National Household Travel Surveys (NHTS), this study involves two large national samples to try to more accurately identify the impact of telecommuting on workers’ travel patterns. Through a series of empirical tests, this research investigates how telecommuting influences workers’ one-way commute trips, daily total work trips, and daily non-work trips, and tries to provide some answers to a question that has been discussed for some years—namely, whether telecommuting and personal travel are complements or substitutes. The results of these tests suggest that telecommuting has been an important factor in shaping personal travel patterns over the 2001–2009 period, and that telecommuting indeed has a complementary effect on not just workers’ one-way commute trips, but also their daily total work trips, and total non-work trips.