Acute headache is a very frequent symptom, responsible for significant demand at primary care units and emergency rooms. In such sets in Brazil, metamizol is easily found but, on the other hand, neither ergotics nor triptans are available. The aim of this study is to compare intravenous metamizol with placebo in the acute treatment of migraine with aura, migraine without aura and episodic tension-type headache. Fifty-four migraine with aura patients, 95 migraine without aura patients and 30 tension-type headache patients were treated with metamizol. Ninety patients (30 migraine with aura, 30 migraine without aura and 30 tension-type headache patients) received placebo. Pain intensity, nausea, aura, photo- and phonophobia were investigated at 30 min and 60 min after the administration of the drug. Significant improvement of pain after 30 min and 60 min post-dosage was achieved from metamizol groups compared with placebo groups. Significant improvement of all other symptoms was achieved after 60 min post-dosage. Side-effects were mild and with small incidence. Metamizol is an effective, safe and low price drug. It may be regarded as a good alternative drug for the treatment of common acute primary headaches.