When entering Tanzania proof of yellow fever vaccination may be required if some one is entering from a country with a risk of yellow fever such as Kenya. People arriving from areas with out yellow fever should not need proof of it. However, a study done last year showed unpredictable checks at borders and even people who were arriving from Europe or Dubai were sometimes checked. Checks were more likely at land borders than at airports and more likely at Arusha than Dar es Salaam and Zanzibar. Consequences of not having a valid certificate or exemption note included fines, clearance after a short discussion, inability to obtain a visa and even vaccination at the border. It seems everyone arriving in Tanzania should either be vaccinated or carry an exemption note. This should be unnecessary for those not entering from endemic countries however after reading the study it seems necessary.