A sexual dimorphism (SD) of the “vertebra prominens” was found, namely the 7th cervical vertebra (C7) spinous process (SP) is more frequently longer in men and the 1st thoracic (T1) SP in women.[1] We assume that the cause of this SD is the different anatomy of the anterior upper thoracic region (AUTR) between men and women, due to the presence of the breast. One-hundred forty-two women aged 48.1Âś17 years old, who visited the OPD for neck complaints, were studied. Measures included the age, the relationship of C7 and T1 SP length, documented in three types (type 1= [C7>T1], 2 = [C7 = T1], 3 = [C7 < T1]), the breast size, (small, medium and large), the length ratio of C7/T1 SP and the BMI. Breast size and SP length relationship between C7 and T1 was found to be significantly correlated. The results confirm that the cause of the SD of the SP length of C7 and T1 seems to be the different female AUTR anatomy due to the presence of the breast and it is probably the result of the need of the posterior cervical anatomical structures to compensate for the higher torque created by the female AUTR anatomy. These original findings are useful in clinical examination, in breast oncology, for the plastic surgeons, in terms of implantation of the proper breast size implant, after mastectomies for malignancies but also for aesthetic reasons and the software of all surface topography devices should be adjusted accordingly.