The total number of reported instances of intermittent hydrarthrosis, including the first case described by Perrin1in 1845, seventy-seven collected or reported by Bierring2and the case presented at this time, is 106.3 The disease has occurred exclusively in the white race, with equal frequency in the male and the female and at an average age between 20 and 45. In some cases the condition has been familial, notably in Blanc's4case of a mother and daughter and the case of three sisters, a brother and a cousin reported by Schlesinger.5In the latter case there was also hemophilia and Quincke's edema in the family, and one person with hemophilia whom I have seen had irregularly recurrent serous effusions in the left wrist and right knee. A complexity of apparently unrelated factors enters into the cause of intermittent hydrarthrosis, the most important being infection, endocrine