A variety of pathophysiological mechanisms and underlying diagnoses may underlie the symptoms and sensory abnormalities among youth with erythromelalgia (EM) or congenital insensitivity to pain (CIP). Quantitative sensory testing (QST) rcould contribute to characterizing different subtypes of EM and CIP, which could potentially facilitate diagnosis and more focused treatment. The aim of this exploratory study is to use QST to phenotype patients with suspected hyposensitivity or hypersensitivity to expand our knowledge, and better categorize different sensory profiles. Four patients with EM and two patients with CIP between 6 and 18 years old from a subset of patients in an ongoing gene discovery study were recruited for QST. Preliminary results highlight the variability in clinical presentation of probands with EM or CIP. Going forward, we hope to further correlate QST findings with gene candidates and other clinical variables among patients with EM and CIP. Efforts are in progress to establish a multicenter data registry/repository for children and adolescents with EM. QST can provide additional information on the sensory function of patients presenting with suspected hypo- and hypersensitivity. In the future, it may help predict or guide treatment choices.