Bodily changes after mastectomy cause psychological disturbances as well as impacts negatively on the self-image of women. This study analysed and compared changes in self-image pre- and post-mastectomy among women with breast cancer in selected hospitals in Southwest Nigeria. A descriptive exploratory design was adopted; purposive sampling was used to select 56 women aged between 18-70 years diagnosed with breast cancer who subsequently had a mastectomy. The study was conducted at the University College Hospital, Ibadan, and Obafemi Awolowo University Teaching Hospital, Ile Ife. Data was collected using two instruments. These were the Breast Impact of Treatment Scale (BITS) and the Situational Discomfort Scale (SDS. Data was analysed using SPSS version 20 using descriptive and inferential statistics. Findings showed that pre-operative self-image scores of respondents ranged from 2 to 39, with a mean of 13.68 ±5.74. None of them had severe distress, however, 77.3% had mild distress; and 22.7 % had moderate distress. During post-mastectomy, the scores ranged from 11 to 62 with a mean of 43.29 ± 5.50. None of the respondents had mild distress but 89.8 % had severe distress while the rest had moderate distress. The study found a significant difference between pre- and post-mastectomy self-image, the pre-operative mean score was 13.68, while the post-mastectomy mean score was 43.26 at p =0.0001, with a t value of -24.78. This study concluded that, while the respondents had mild self-image distress before mastectomy, severe distress was attributed to post-mastectomy periods.