My husband & I have made this trip 3 times. Yellow Fever is not the problem. But the mosquitos carry Malaria there. We have never gotten shots for it even though our Dr. recommended them this last time which was A Nov. 10- 01 sailing. If you were to take a walk (tour)through the forrest of Costa Rica you might consider the shots. Just take a can of Johnson's Mosquitos "off". Otherwise it should not be a problem.