We sought to investigate whether intensity-modulated radiotherapy (IMRT) has a dosimetric advantage compared to the standard wedged tangential technique (SWT) for whole-breast radiotherapy (WBRT) in Asian women with relatively small breast volume. Computed tomography images of 25 Asian patients with early-stage breast cancer (right 15, left 10) used for WBRT planning were examined. After contouring the target volumes and bilateral lungs and, for left-side treatment, the heart, 4 plans were made for each patient: namely, SWT, tangential-field IMRT (T-IMRT), 3-field IMRT (3F-IMRT), and 4-field IMRT (4F-IMRT). The prescribed dose was 5000 cGy. The median planning target volume (PTV) for WBRT was 552.6 cc (range 288.8-1518.4 cc). Compared to SWT, (1) T-IMRT achieved significant improvement for dose homogeneity in the PTV (p < 0.001) and the dose received by 2% (D2) of the PTV (p < 0.001). T-IMRT also reduced the bilateral lung mean dose (p < 0.001) and the ipsilateral lung volume which received more than 20 Gy (V20) (p = 0.01). (2) 3F-IMRT resulted in a significant increase in the mean dose to the ipsilateral lung (p < 0.001) and to the contralateral lung (p < 0.001). (3) 4F-IMRT also resulted in a significant increase in the mean dose to the ipsilateral lung (p < 0.001) and to the contralateral lung (p < 0.001). Tangential-field IMRT provided an improved dose distribution compared with SWT for WBRT in Asian women with a relatively small breast volume.