Following a report by Professor Charles Sultan, a pediatric endocrinologist at Montpellier University Hospital, regarding an increase in the number of cases of severe malformations affecting the male genital tract (hypospadias, cryptorchidism, micropenis, pseudohermaphroditism), observed in his department over the past two years, the DGS referred the matter to the InVS to investigate this issue. Furthermore, Professor Sultan noted that these cases “occurred in families of farmers or individuals potentially exposed to chemicals.” Given the data from experimental studies highlighting the toxic effects of certain xenobiotics on reproductive function, the first part of the study focused on an in-depth descriptive analysis of these cases, including an investigation into specific environmental exposures. Furthermore, an assessment of the plausibility of a link between the reported cases and the insecticide spraying carried out in 2000 as part of efforts to combat the spread of the West Nile virus was conducted. The second part of the study consisted of determining whether the presence of an excess of congenital malformations of the male genital tract in the Languedoc-Roussillon population was plausible by comparing the prevalence in this region to the national average. Prevalence was estimated using hospitalization data for cryptorchidism and hypospadias of all types, treated in pediatric surgery departments of public and private healthcare facilities. Cases were identified using the PMSI database from 1998 to 2001. A case was defined as a hospital stay for surgical treatment of cryptorchidism or hypospadias in a child under 7 years of age as of December 31, 2001, residing in the region under study. Hospital stays were described based on age at the time of surgery and diagnostic codes. Crude rates of surgically treated malformations per 1,000 boys were calculated. Age-standardized rates were calculated using the French population as the reference population and compared to the estimated average rate for France. Age-standardized surgery rates vary across regions from 17 to 32 per 10,000 for cryptorchidism and from 4.9 to 12.8 per 10,000 for hypospadias. They remained relatively stable over the 1998–2001 period, though with geographical variability. In the Languedoc-Roussillon region, the rates of surgical treatment for external genital malformations are close to the average rates calculated for France for hypospadias and cryptorchidism. Several hypotheses can be considered to explain the increase in the number of cases reported between 1998 and 2000 at the Montpellier University Hospital, such as local variations in healthcare availability and surgical practices, or the growing reputation of the hospital’s pediatric endocrinology department. Furthermore, the descriptive analysis of these cases could not identify any particular exposure or specific environmental risk factors based on the exposure data provided. Finally, it should be noted that no spraying for mosquito control is authorized in the Camargue, a protected area, including for the control of the West Nile virus. (R.A.)