OBJECTIVE To report on the first use of a quality‐of‐life (QoL) measure specific for erectile dysfunction (ED), the ‘ED effect on QoL’ (ED‐EQoL), to assess the effect of ED on QoL after radical prostatectomy (RP). PATIENTS AND METHODS We retrospectively identified 89 patients who had undergone RP at one institution. Each was sent the ED‐EQoL and a second questionnaire asking whether they had been counselled before RP about possible ED afterward. RESULTS The response rate was 91% and the median time since RP 92 months; 76% of those who were potent before RP were impotent afterward. The overall results showed that the QoL of 72% of patients was moderately or severely affected. For each question, on average a third of the patients reported that their QoL was affected either ‘quite a lot’ or ‘a great deal’. CONCLUSIONS This study shows that ED after RP has a profound effect on QoL; it is therefore important when assessing ED to use an ED‐specific QoL questionnaire such as the ED‐EQoL to measure the psychosocial effect of ED, in addition to using an instrument such as the International Index of Erectile Function to measure the functional aspects of ED.