This paper discusses the role of small area spatial analysis of birth defects in environmental surveillance. Two approaches are reviewed: (1) the investigation of identified geographically localised potential environmental hazards, and (2) the detection of clustering. Examples are given where these 2 types of investigation have been used in the follow-up of individual clusters. Finally, it is argued that environmental surveillance, incorporating the 2 groups of spatial methods, should become a part of public health practice on both proactive and reactive basis.