Experimental animal studies show that measurement of anogenital distance (AGD) and/or penis length may provide lifelong ‘read‐outs’ of foetal androgen exposure during the masculinization programming window (MPW). However, variation in postnatal androgen exposure may complicate interpretation of such measurements. This is important to clarify if such measurements are to be applied to humans. The present aim was to evaluate effects of prenatal and/or postnatal manipulation of androgen production/action on growth of AGD and the penis in rats. Pregnant rats were treated daily before (e13.5–e21.5) and after birth (postnatal days 1–15) with either vehicle, 500 mg/kg di(n‐butyl) phthalate (DBP) or 100 mg/kg flutamide (postnatal only) in prenatal + postnatal treatment combinations (N = 6 treatment combinations); DBP impairs androgen production whereas flutamide impairs androgen action. Male offspring were killed on postnatal day 8 (prepuberty), 25 (early puberty) or 90 (adulthood) when AGD was measured, the penis dissected out and its weight and length measured; plasma testosterone and ventral prostate weight were measured at day 90 to assess endogenous androgen exposure. In controls, penis length, girth and AGD increased 2.2‐, 5.3‐and 5.9‐fold respectively from day 8 to day 90. Significant inhibition of penis growth and final length and girth was induced by treatments that inhibited postnatal androgen action. Conversely, growth and ultimate (adult) AGD was inhibited by prenatal inhibition of androgen production whereas postnatal androgen inhibition had negligible effect. Nevertheless, AGD and penis length were highly correlated at every age (R² > 0.33; p < 0.0001). However, altered endogenous androgen exposure may confound interpretation of changes in adults exposed prenatally/postnatally to DBP/flutamide. We conclude that AGD provides a lifelong guide to prenatal androgen exposure (in the MPW) whereas penis size reflects both prenatal + postnatal androgen exposure. At the group treatment level, prepubertal measurement of either AGD or penis size accurately predicts their size in adulthood.