The term “pneumaturia” signifies the passage of gas from the bladder during micturition or on catheterization. Secondary pneumaturia is not uncommon and results from the introduction of atmospheric air into the bladder by instrumentation or the passage of gas from a hollow viscus through a fistulous opening into the bladder. Primary pneumaturia is rare and is due to fermentation of urine in the bladder through the agency of some fermenting organism. Cases of primary pneumaturia may be subdivided into two groups, depending upon whether or not the urine contains glucose. The extremely small number of cases of primary pneumaturia on record, the almost total absence of discussion of this subject in the roentgenologic literature, and the fact that the roentgen examination offers probably the easiest method of diagnosis are justification for the present report. Only four references (1–4) could be found to the roentgen diagnosis of primary pneumaturia. The two cases to be reported here constitute, therefore, the fifth and sixth in which the diagnosis was established or confirmed roentgenologically. They are the ninth and tenth examples of primary pneumaturia to appear in the American literature (Table II). The earliest mention of a case of pneumaturia appeared in 1671 in a publication called “Curiosities of Nature.” Raciborski's (5) Latin quotation from the original article was translated by Taussig (6) as follows: “A leading citizen of Gotha was afflicted by anal colic, with rumbling tension in the abdomen, pain about the navel and, what is strange, wind was passed by the penis, as if through the usual and accustomed channel, sometimes with and sometimes without urine.” The first detailed case reports of the condition were those of Raciborski in 1860 (5) and Keyes in 1882 (7). Guiard (8) and Duménil and Guiard (9), in 1883, were the first to point out the relationship between pneumaturia and diabetes mellitus, suggesting that the pneumaturia resulted from fermentation of glucose within the bladder. Mulsow and Gillies (2), however, were impressed by the rarity of pneumaturia in diabetics, in spite of the fact that the colon bacillus, which readily ferments glucose, is so frequently found in the urine of diabetic patients. Arthur and Johnson (3) believe that the following conditions must in general be present to cause primary pneumaturia: bacteriuria (E. coli being the only organism common to all cases), glycosuria, albuminuria, pyuria, and residual urine. It is pointed out by these writers that the method of gas production by E. coli is unknown. The urine, they believe, may contain a substance capable of being split by fermentation with the production of an insoluble gas. Pneumaturia does not result from the ordinary ammoniacal fermentation of urine or from putrefactive decomposition because the hydrogen sulfide gas which is formed is soluble in urine.