Concomitant comorbidity is a key factor in treatment decision-making for breast cancer. The aim of this study was to determine how the Charlson Comorbidity Index (CCI) affected treatment and risk of mortality of women with TNBC, the subtype with the poorest prognosis. We accessed 20 177 cases of TNBC from the California Cancer Registry 2000-2015 with documented Charlson Comorbidity Index (CCI). Cox Regression was used to compute the adjusted risk of breast cancer-specific mortality for a CCI of 1 (low comorbidity) and 2+ (high comorbidity) vs a CCI of 0 (no comorbidity). Logistic regression was used to compute the association of CCI with treatment of mastectomy, lumpectomy + radiation, and chemotherapy. Analyses were conducted separately for each stage. Patients with high comorbidity CCI (2+) were less likely to receive systemic chemotherapy irrespective of Stage. High comorbidity was associated with higher breast-specific mortality in all stages of disease. High comorbidity did not have an effect on the use of lumpectomy and radiation of stage 1 breast cancer but was associated with reduced use in stages 2-4. Comorbidity was not associated with decreased risk of mastectomy except for patients with high comorbidity in stage 3. Concomitant comorbidity influences treatment decisions and breast cancer-specific mortality in patients with TNBC.