The pattern of intrathoracic Hodgkin's disease assessed by computed tomography. Computed tomography (CT) was used to define the sites of intrathoracic abnormality in Hodgkin's disease, determine a pattern of progression of disease in the thorax, and establish the place of this pattern of spread in the differential diagnosis of thoracic abnormalities. One hundred eight patients with newly diagnosed Hodgkin's disease were studied by chest CT. Seventy-seven patients had intrathoracic abnormalities. The pattern seen was one of contiguous spread from the anterior mediastinal/paratracheal area to the other mediastinal lymph node groups (aortopulmonary, subcarinal, posterior mediastinal, and internal mammary), to the hila, and then into the lung by extension or as discrete nodules. Involvement of the pleura, pericardium, or chest wall occurred only after the anterior mediastinal/paratracheal mass had enlarged to greater than 30% of the thoracic diameter. The probability that this pattern of contiguous lymph node spread occurred by chance alone was very small. Hodgkin's disease spreads from the anterior mediastinal/paratracheal area in a contiguous manner. Exceptions are unusual enough that when they occur, diagnoses other than Hodgkin's disease are more likely. 