Vertical transmission of dengue-1 virus was demonstrated over 3 consecutive generations of Aedes albopictus by tracing descendants of individual, vertically infected females. This study is the first to examine efficiency of vertical transmission of a flavivirus by vertically infected mosquitoes. Vertically infected Ae. albopictus females were more efficient vertical transmitters than females infected by inoculation (i.e., horizontally). Three of 4 vertically infected females examined transmitted virus to their offspring, whereas less than or equal to 0.7% of females infected by inoculation were capable of vertical transmission.