Objective. To evaluate the correlation between International Index of Erectile Function (IIEF) questionnaire scores, nocturnal penile tumescence parameters and sildenafil response in patients with erectile dysfunction using a minimal investigations approach. Material and methods. A total of 97 patients without any risk factors for erectile dysfunction were included. After completing the IIEF questionnaire, nocturnal penile tumescence monitoring was performed in all patients for 1 or 2 nights. Subsequently, sildenafil was given at a dosage of 50 or 100 mg according to the response. The relationship between nocturnal penile tumescence results, the severity of erectile dysfunction according to the IIEF questionnaire and sildenafil response was evaluated using Pearson's χ2 test. Results. Based on the questionnaire scores, 25 patients (25.8%) had mild, 44 (45.4%) had moderate and 28 (28.8%) had severe erectile dysfunction. Forty-four patients (45.4%) had normal and 53 (54.6%) had abnormal parameters after nocturnal penile tumescence recording. The sildenafil response was positive in 63 patients (64.9%) who were given 50 mg and in 26 (26.8%) who were given 100 mg. However, eight patients (8.2%) did not respond to sildenafil. While the severity of erectile dysfunction according to IIEF scores and the sildenafil response did not show any correlations with nocturnal penile tumescence results, there was a statistically significant relationship between sildenafil response and the severity of erectile dysfunction. Conclusion. Changing concepts in the evaluation of ED have resulted in the use of effective therapeutic applications consistent with the degree of symptoms of patients without the waste of time caused by performing expensive, invasive, ineffective and time-consuming diagnostic tests. © 2006 Taylor & Francis.