OBJECTIVE To underline peculiar composition of kidney stones and to propose an epidemiologic study of urinary stones in West African countries, where epidemiologic studies are scarce. Only few data are available regarding stone composition in sub-Saharan countries. Recently, a set of 100 stones consecutively removed by surgery in the Department of Urology of the University Hospital of Ouagadougou in Burkina Faso were collected for physical analysis, which provided the opportunity to obtain an epidemiologic profile of stone composition in this country. MATERIALS AND METHODS A total of 100 stones from 64 men, 22 women, 10 boys, and four girls were analyzed by morphologic examination, infrared spectroscopy, and electron microscopy in our laboratory. The results were considered by sex and separately for adults and children. RESULTS Sixty-five percent of the 100 stones contained calcium oxalate as the main component. Interestingly, the second main component was opaline silica (18%). Furthermore, opaline silica was identified in any proportion in 48% of the stones. The prevalence was sex and age dependent. Opaline silica was detected as the main component in 42% of the nuclei, which underlines its role as one of the main components involved in the initiation of calculi in this country. CONCLUSION For the first time, a dramatically high occurrence of a ``scarce'' urinary stone component, namely opaline silica, was reported in a series of consecutive calculi from a single country. We propose that a regular consumption of clay could be the origin of this phenomenon in these populations.