In late 2007, a general practitioner practicing in the town of Sinnamary in French Guiana reported an unusually high number of cases of thyroid disorders among his patients. This report was investigated by the Antilles-Guyana Interregional Epidemiology Unit (Cire Antilles-Guyana) using the method for the assessment and management of spatio-temporal clusters of non-infectious diseases published by the French Institute for Public Health Surveillance (InVS). The study period spanned from January 2002 to April 2008. A total of 26 individuals met the case definition; the male-to-female ratio was 0.44, and the median age was 44 years [min=19; max=73]. An increase in the number of cases was observed starting in 2006 and particularly in 2007. The annual incidence rates of hyperthyroidism, nodules, and goiters were higher among women than among men, at 0.92, 1.11, and 0.74 per 100,000 inhabitants for women versus 0.46, 0.37, and 0.09 per 100,000 inhabitants for men. A comparison with data from the SU.VI.MAX study conducted in France shows higher annual incidence rates of hyperthyroidism in Sinnamary. This study did not identify any specific factor causing a common exposure that could explain the increase in the number of diagnosed thyroid conditions in Sinnamary between 2002 and 2008. The diversity of the diagnoses made and the fact that these conditions are multifactorial do not allow us to rule out the possibility that this cluster is due to chance. The increase in the number of cases did not continue after 2009. Monitoring in collaboration with the reporting physician is proposed to track the evolution of the health situation.