Illegal logging is a globally important issue, but there is dearth of quantitative information on the spatial and temporal patterns of illegal logging on the ground. We measured the size, species, and ages of stumps from illegally or legally logged trees along a total of 10 km of 20-m-wide transects in traditional production forests of Myanmar. The number and basal area of stumps resulting from illegal logging were 9.93- and 3.89-fold greater, respectively, than those of legal logging. Illegal logging always targeted high-quality trees for timber, but it increased significantly after legal logging. Spatial patterns of illegal logging varied before, during and after legal logging. More illegal logging occurred in areas that were closer to old footpaths before legal logging, but more illegal logging occurred closer to main and logging roads after legal operations. We conclude that current legal logging operations facilitate illegal logging because the construction of logging roads makes it easier for illegal loggers to transport their harvests. Therefore, the government should enforce existing rules that require that logging roads be decommissioned and rendered impassable after the cessation of legal logging operations.