The aim of this study was to analyse the effect of a nursing intervention in increasing the therapeutic self-care demand in patients with breast cancer-related lymphedema after a mastectomy. The pre-experiment was carried out on women in the State Cancer Institute in Colima, Mexico. Thirty women who had undergone a mastectomy were included in this study. Each woman received a nursing intervention to increase her knowledge, skills and motivation, which are the components of therapeutic self-care demand. Students’ t and P values were calculated for paired means, and the McNemar X2 test was performed for paired categorical variables. It was found that Students’ t values for therapeutic self-care demand, knowledge, skills and motivation were significant (all with P = 0.00001). It was also found that McNemar X 2 values for the same criteria paired categorically were significant (P = 0.0002, P = 0.003, P= 0.0002, P = 0.00001, respectively). It was concluded that the nursing intervention was effective in increasing the therapeutic self-care demand of patients with post-mastectomy breast cancer.