The psychological study of masculinity (M) and femininity (F) throughout the twentieth century shows two very different approaches. In the first half of last century, authors try to test the bipolar continuum hypothesis, whereas during the second half, the hypothesis of two orthogonal dimensions predominates. Empirical studies carried out in various countries with the classic M and F scales show that the data do not support: a) the bipolar continuum hypothesis; b) the close relationship between masculinity/men and femininity/women as the single pattern of functional development; and c) the convergence validity of the different assessment instruments. In turn, the empirical results obtained with the new M and F scales show: a) the multidimensionality instead of bi-dimensionality of the different scales; b) that the different M and F scales are not equivalent; and c) that there is no theory capable of guiding the development of new scales to assess these constructs. At the beginning of the 21st century, after the critical evaluation of the studies carried out during about 100 years, we face a critical question: is it worthwhile to continue talking about M and F within the field of science and, more specifically, within the field of psychology?