Dutch slave traders brought yellow fever to the Americas from Africa during the mid-seventeenth century. For the next two and a half centuries, the disease terrorized seaports throughout the Americas. Proof of the mosquito hypothesis was delayed because of two aspects of the disease: patients are viremic only during the first several days of clinical illness, and most mosquitoes require about 2 weeks of viral incubation before becoming infectious. Control of Aedes aegypti in urban centers failed to eliminate the disease because of its transmission by tree-hole-breeding mosquitoes that spend their winged lives mainly in forest canopies. Yellow fever continues to be a significant public health problem in parts of South America and Africa.