Larvae of Aedes albopictus, a mosquito known for transmitting dengue virus, were identified in the city of León, Nicaragua, in 2003. Mosquito larvae were collected from a total of 2,225 residences in the 2 largest cities in Nicaragua during the period from June to September of 2003, and larval Ae. albopictus were identified in 4 homes in León. This represents the 1st detection of Ae. albopictus in a major Nicaraguan urban center, and increased control efforts appear to have eliminated the mosquito subsequently from León. The presence of Ae. albopictus in urban Nicaragua highlights the need for surveillance of areas thought to be free of the mosquito so that early detection and control activities can prevent its spread.