Three-dimensional (3D) reconstruction can be used to study the structural relationships between various tissue components and can help in the understanding of disease processes. Examples of perineural invasion have been reconstructed in two cases of adenocarcinoma of the extrahepatic bile duct. Ninety-six serial 5 pm sections were taken from both cases stored on file and 3D images were constructed using a Kontron VIDAS image analysis system. Both cases showed continuity of tumour cells within the perineural space. The isolated islands of malignant glands seen by conventional microscopy were shown to be in continuity with larger tumour cell masses via a complex branching network. In addition, direct continuity was demonstrated between malignant glands within the perineural space and those within the surrounding stromal tissue. During growth, the tumour appeared to have followed the plane of least resistance, although the availability of the perineural space may itself have been shaped by pressure effects and/or proteolytie enzyme secretion. Threedimensional reconstruction of perineural invasion in adenocarcinoma of the extrahepatic bile ducts shows the value of this technique in demonstrating the structural relationships between the tumour and the host nerve bundle.