We assessed the efficacy and safety of oral single doses of 0.5 and 1 g metamizol vs. 1 g acetylsalicylic acid (ASA) in 417 patients with moderate episodic tension-type headache included in a randomized, double-blind, placebo- and active-controlled, parallel, multicentre trial. Eligibility criteria included 18–65 years of age, history of at least two episodes of tension-type headache per month in the 3 months prior to enrolment, and successful previous pain relief with a non-opioid analgesic. Treatment arms were metamizol 0.5 g (n = 102), metamizol 1 g (n = 108), ASA 1 g (n = 102) and placebo (n = 105). The analgesic efficacy of 0.5 and 1 g metamizol vs. placebo was highly statistically significant (α: 0.025; one-sided) for sum of pain intensity differences, maximum pain intensity difference, number of patients with at least 50% pain reduction, time to 50% pain reduction, maximum pain relief and total pain relief. A trend towards an earlier onset of a more profound pain relief of 0.5 and 1 g metamizol over 1 g ASA was noticed. All medications including placebo were almost equally safe and well tolerated.