High mammographic density (MD) is a well-known risk factor for breast cancer (BC). However, there is limited data on the relationship between MD and molecular subtypes of BC. The aim of this study is to investigate the possible association of MD with molecular BC subtypes. The medical records of 203 women who underwent surgery for BC were retrospectively evaluated. MD was categorized as low dense and high dense. The two groups were compared between each other in terms of all clinicopathological characteristics. Mammography revealed “low dense” breast in 105 (51.7%) patients, while 98 (48.3%) patients had “high dense” breast. Luminal A/B, HER2, and triple-negative tumors were found in 174 (85.7%), 9 (4.4%), and 20 (9.9%) patients, respectively. Patients with high MD had significantly more common nodal metastasis, advanced stage, multifocality, and higher grade. Estrogen receptor positivity was more common in patients with low MD, whereas high MD was significantly more common in triple-negative cancers compared with non-triple-negative cancers. The positive association of high MD with nodal metastasis, advanced stage, multifocality, higher grade, and triple-negative molecular subtype is of great importance for the aggressiveness of the BC.