This research examines the effectiveness of problem-based learning (PBL) in an online geographic information systems (GIS) course for adult learners. Adults expect to take greater control of their learning and tend to be self-directed. Students are encouraged to take an active role as problem-solvers in PBL courses. The effectiveness of PBL in face-to-face courses has been shown. Effectiveness in online courses is demonstrated in this study. The performance and experiences of students and instructor in two online courses are compared. The results show that PBL can be more engaging than traditional methods, making PBL-GIS a good choice for an online adult audience. (Contains 6 tables and 3 figures.)