This study evaluates osmophobia (defined as an unpleasant perception, during a headache attack, of odours that are non-aversive or even pleasurable outside the attacks) in connection with the diagnosis of primary headaches. We recruited 775 patients from our Headache Centre (566 females, 209 males; age 38+/-12 years), of whom 477 were migraineurs without aura (MO), 92 with aura (MA), 135 had episodic tension-type headache (ETTH), 44 episodic cluster headache (ECH), 2 chronic paroxysmal hemicrania (CPH) and 25 other primary headaches (OPHs: 12 primary stabbing headaches, 2 primary cough headaches, 3 primary exertional headaches, 2 primary headaches associated with sexual activity, 3 hypnic headaches, 2 primary thunderclap headaches and 1 hemicrania continua). Among them, 43% with MO (205/477), 39% with MA (36/92), and 7% with CH (3/44) reported osmophobia during the attacks; none of the 135 ETTH and 25 OPH patients suffered this symptom. We conclude that osmophobia is a very specific marker to discriminate adequately between migraine (MO and MA) and ETTH; moreover, from this limited series it seems to be a good discriminant also for OPHs, and for CH patients not sharing neurovegetative symptoms with migraine. Therefore, osmophobia should be considered a good candidate as a new criterion for the diagnosis of migraine.