Purpose: To study the risks of early and late radiogenic lung damage in breast cancer patients after conformal radiotherapy. Methods and Materials: Radiogenic lung sequelae were assessed prospectively in 119 patients by means of clinical signs, radiologic abnormalities, and the mean density change (MDC) of the irradiated lung on CT. Results: Significant positive associations were detected between the development of lung abnormalities 3 months or 1 year after the radiotherapy and the age of the patient, the ipsilateral mean lung dose (MLD), the radiation dose to 25% of the ipsilateral lung (D 25%) and the volume of the ipsilateral lung receiving 20 Gy (V 20 Gy). The irradiation of the axillary and supraclavicular lymph nodes favored the development of pneumonitis but not that of fibrosis. No relation was found between the preradiotherapy plasma TGF-β level and the presence of radiogenic lung damage. At both time points, MDC was strongly related to age. Significant positive associations were demonstrated between the risks of pneumonitis or fibrosis and the age of the patient, MLD, D 25%, and V 20 Gy. A synergistic effect of MLD, D 25%, and V 20 Gy with age in patients older than 59 years is suggested. Conclusion: Our analyses indicate that the risks of early and late radiogenic lung sequelae are strongly related to the age of the patient, the volume of the irradiated lung, and the dose to it.