_The Genito-urinary System._—Albuminuria begins to appear about the second day and tends steadily to increase in amount. Various types of tube casts, often bile-stained, are abundant. The urine shows neither bile nor blood cells except in the later stages of the disease. The reaction is very acid. It is of the utmost importance to note the quantity of urine voided, as scanty secretion, leading to anuria, makes for a very grave prognosis. DIAGNOSIS The main points to consider in the diagnosis are: (1) the facies, (2) the severe cephalalgia and rachialgia, (3) the early albuminuria, (4) the epigastric tenderness, (5) Faget’s law of lack of correlation between pulse and temperature, (6) the absence of clouding of the consciousness, and finally the late appearance of the jaundice and haemorrhages. Of the greatest importance is the history of the case as to recent whereabouts and associates. Also careful questioning as to prior attacks of jaundice or albuminuria related to hepatic or renal diseases. Influenza in its sudden onset and fever and pains has much in common with yellow fever. Weil’s disease is much like yellow fever. The diseases with which yellow fever is most apt to be confused are: _Aestivo-autumnal Malaria._—In ordinary aestivo-autumnal malarial paroxysms the search for the malarial parasite is of great importance, although the finding of a malarial infection does not exclude yellow fever. Albuminuria is not a feature of tropical malaria. In that type of tropical malaria known as bilious remittent fever the clinical picture is rather asthenic and bile pigment in the urine is an early feature. Again jaundice comes on fairly early and the slow pulse is absent. The spleen is enlarged and tender. _Blackwater Fever._—This is an asthenic disease with marked and very early jaundice. The haemoglobinuria (Blackwater) is pathognomonic. Splenic tenderness is marked. _Smallpox._—The early headache, backache and vomiting of smallpox may well confuse one before the eruption of variola appears. _Dengue._—This is probably the most difficult disease to diagnose from yellow fever. The facies, orbital pains and backache of yellow fever and dengue are similar. Dengue also shows a slowing of the pulse. The high blood pressure of the onset is not present in dengue. There is no albuminuria in dengue and there is a marked and early leukopenia with reduction of the polymorphonuclear percentage, which does not exist in yellow fever. The jaundice of yellow fever and the eruption of dengue do not show themselves until after the first three days. Relapsing fever, typhus fever and plague have been considered by some authorities as possible of confusion with yellow fever.