In colloquial English, a “grower” is a man whose phallus expands significantly in length from the flaccid to the erect state; a “shower” is a man whose phallus does not demonstrate such expansion. We sought to investigate various factors that might predict a man being either a grower or a shower. A retrospective review of 274 patients who underwent penile duplex Doppler ultrasound (PDDU) for erectile dysfunction between 2011 and 2013 was performed. Penile length was measured, both in the flaccid state prior to intracavernosal injection (ICI) of a vasodilating agent (prostaglandin E1), and at peak erection during PDDU. The collected data included patient demographics, vascular, and anatomic parameters. The median change in penile length from flaccid to erect state was 4.0 cm (1.0–7.0), and was used as a cut-off value defining a grower (≥4.0 cm) or a shower (4.0 cm). A total of 73 men (26%) fit the definition of a grower (mean change in length of 5.3 cm [SD 0.5]) and 205 (74%) were showers (mean change in length of 3.1 cm [SD 0.9]). There were no differences between the groups with regards to race, smoking history, co-morbidities, erectile function, flaccid penile length, degree of penile rigidity after ICI, or PDDU findings. Growers were significantly younger (mean age 47.5 vs. 55.9 years, p < 0.001), single (37% vs. 23%, p = 0.031), received less vasodilator dose (10.3 mcg vs. 11.0 mcg, p = 0.038) and had a larger erect phallus (15.5 cm vs. 13.1 cm, p < 0.001). On multivariate analysis, only younger age was significantly predictive of being a grower (p < 0.001). These results suggest that younger age and single status could be predictors of a man being a grower, rather than a shower. Larger, multicultural and multinational studies are needed to confirm these results.