Introduction: Several questionnaires have been developed for screening cannabis use disorder in clinical populations, but very few studies have compared the screening abilities of the different instruments. Here, we aimed to confirm the psychometric properties of a French version of the Cannabis Use Disorder Identification Test—Revised (CUDIT-R), and to compare its screening abilities with those of the Cannabis Abuse Screening Test (CAST), in subjects consulting in mental health settings. Methods: Two hundred and thirteen cannabis smokers who sought treatment for any type of mental disorder, recruited in four French centres, completed the French CUDIT-R (CUDIT-R-Fr) and the full version of the CAST, and were assessed for Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria of cannabis use disorder by an addiction specialist. They were retested with the CUDIT-R-Fr after approximately a week. The factorial construct validity, internal consistency and test–retest reliability of the CUDIT-R-Fr were assessed. The compared sensitivity and specificity of the CAST and CUDIT-R-Fr were explored, using the clinician assessment as the reference. Results: The French CUDIT-R showed a good internal consistency (Cronbach's alpha = 0.89) and an excellent test–retest reliability (ρ = 0.97). The sensitivity and specificity for screening cannabis use disorder were 0.81 and 0.77 for the CUDIT-R, and 0.92 and 0.63 for the CAST, respectively. Conclusions: Based on the recommended cut-offs, the CAST appeared more sensitive, while the CUDIT-R was more specific, for screening cannabis use disorder in a population of cannabis users with heterogeneous types of mental health disorders.