Mastocytosis patients often experience a number of symptoms, including mastocytosis-associated pain that is difficult to manage due to resistance to usual antalgic treatments and/or the patient’s poor tolerance. Mastocytosis patients display significantly higher levels of indoleamine-2,3-dioxygenase-1 (IDO1) activity, leading to hyperactivation of the N-methyl-D-aspartate receptor. As cannabidiol (CBD) is known to inhibit IDO1′s enzymatic activity, we hypothesized that pharmaceutical-grade CBD is an effective treatment for mastocytosis-associated pain. Patients with non-advanced mastocytosis and refractory pain were eligible for inclusion in this observational pilot study. CBD was initiated at 50 mg/day and increased to a maximum of 900 mg/day. Pain was scored on a 0-to-10 numerical rating scale (NRS). A total of 44 patients were included over a 2-year period. The median dose of CBD prescribed was 300 mg/day (range: 50–900 mg/day). Elevated liver enzymes were observed in one patient. The mean ± standard deviation NRS pain score decreased significantly from 7.27 ± 1.35 before treatment to 3.78 ± 1.99 after 3 months of treatment (p < 0.0001). Fifteen patients (34%) were able to discontinue all their previous antalgic medications. CBD treatment might be a safe, effective treatment for mastocytosis-associated pain and its use requires confirmation in a randomized, controlled trial.