In the study I will discuss today, we investigated the shape of the mortality function before age 50. The analysis covered 1,334 mortality functions from eight countries over a century and a half, with different data sets for the two sexes. Our analysis was performed by applying a non-parametric technique to the life tables of the Human Mortality Database. This allowed the identification of the critical points – the minima and maxima – of the mortality function. We used this information to analyze the rise and fall of mortality which takes place between puberty and the onset of demographic ageing, generally known as the “mortality hump.” From our study four major results emerge: a) The mortality hump is not a universal phenomenon; b) Its amplitude is generally larger in males than females and in both sexes it shows a secular decline; c) Its length is similar in males and females and it has shown minor variation over the last 150 years; and d) The hump occurs earlier in females than in males, and in both sexes its location shows a secular shift towards younger ages. Our finding appears to be supportive of the testosterone hypothesis, which claims that the mortality hump reflects the rise of testosterone levels during puberty and the subsequent falls through adulthood.