Radiation therapy played a classic role in the radical treatment of localized Hodgkin's disease. We described a Hodgkin's disease patient, stage ⅡA, who was found a left lung mass on a chest film 2 months after irradiation. The mass was near the left lower heart border and obliterated the left diaphragm silhouette. Because the location was quite different from the commonly recognized paramediastinal radiation pneumonitis following mantle-field irradiation, the lesion has been mistakenly interpreted as a recurrent tumor or tuberculoma. After reviewing and comparing the chest radiograph with the subdiaphragmatic port-film, a diagnosis of radiation pneumonitis due to spleen irradiation was suspected. Given only symptomatic treatment, the mass spontaneously resolved 3 months later. The unusual case highlighted the importance of knowledge of the radiationport arrangement on the correct interpretation of a follow-up chest radiograph in Hodgkin's disease patients receiving radiotherapy.