Filariasis has long been known to be prevalent in St. Croix, but there has been little reported from the neighbouring island of St. Thomas. The purpose of this article is to present the results of limited observations made during the course of leprosy field studies in the two islands during the years 1939 and 1940. I. GENERAL INFORMATION ABOUT ST. THOMAS AND ST. CROIX St. Thomas and St. Croix are two of the American Virgin Islands and are located to the east and south-east of Puerto Rico at approximately 18 degrees north latitude and 64 degrees west longitude. St. Croix, which lies in the Caribbean about 40 miles south of St. Thomas, is 21 miles long and 6 miles wide with a total area of about 84 square miles. St. Thomas, which is 13 by 3½ miles in extent and has a land area of 32 square miles, is more rugged and hilly, with little level land.