This case study is available in English. It is intended for advanced level health care providers, especially pediatricians, of the special susceptibilities of children to hazardous substances in the environment and aid in their evaluation of potentially exposed patients. This case study provides information related to clusters including: case definition, case confirmation, population denominator, exposure assessment, plausible hypotheses, risk communication, and resources. Upon completion of this case study the participant should be able to define a disease cluster, describe the components of the public health department disease cluster investigation, and describe the physician's responsibility regarding disease clusters. The CDC designates this educational activity for a maximum of 1.5 hours toward the American Medical Association (AMA) Physician's Recognition Award, 1.6 contact hours in nursing, and 0.1 Continuing Education Units (CEUs).