PURPOSE Basal thumb joint osteoarthritis frequently coexists with carpal tunnel syndrome. The two conditions have traditionally been treated surgically through separate incisions. We sought to determine whether carpal tunnel release using a single incision during basal joint arthroplasty is as effective as a two-incision approach in patients with concomitant carpal tunnel syndrome and basal thumb joint osteoarthritis. METHODS For this purpose, 40 patients were randomly allocated to either a single-incision or double-incision approach, all of whom completed the full follow-up period. The Boston Carpal Tunnel Questionnaire, QuickDASH, and a 10-point visual analog scale pain-severity rating were obtained from patients 3, 6 and 12 months post-operatively. RESULTS The two treatment groups experienced comparable, progressive improvement in all symptom-, function-, and pain-related outcomes, with mean surgery time significantly shorter with the single-incision approach, and four versus zero patients in the double-incision group developing pillar pain (p = 0.035). CONCLUSIONS Concomitant basal thumb joint osteoarthritis and carpal tunnel syndrome might be effectively performed through a single-incision approach, potentially avoiding any morbidity classically associated with a second incision. LEVEL OF EVIDENCE Level II/Therapeutic Study. TRIAL REGISTRATION ClinicalTrials.gov: NCT04391751, 04/29/2020, retrospectively registered.