Serotonin (5-HT) plays a major role in the pathophysiology of primary headaches. The presynaptic 5-HT uptake mechanism, which is important for the regulation of 5-HT levels in the neuronal synapses, can be examined indirectly by measuring the number of 5-HT transporters in membranes from platelets. The aim of the present study was to investigate the platelet 5-HT transport system in patients with primary headache disorders. Bmax, an index of the number of platelet 5-HT transporters, was measured in 40 patients with chronic tension-type headache, in 30 patients with migraine without aura, and in 40 healthy controls using a binding analysis with tritiated paroxetine as the ligand. The Bmax was 664 (589–846) (median (quartiles)) fmol/mg protein in patients with tension-type headache and 662 (534–781) fmol/mg protein in healthy controls, P= 0.40. The Bmax was 675 (558–747) fmol/mg protein in patients with migraine, which was not significantly different from the Bmax in controls, P= 0.94. In conclusion, the present results indicate that the number of platelet 5-HT transporters is normal in patients with chronic tension-type headache and in patients with migraine without aura.