Background: Computerized versions of well-established measurements such as the PHQ-9 are widely used, but data on the comparability of psychometric properties are scarce. Objective: Our objective was to compare the interformat reliability of the paper-and-pen version with a computerized version of the PHQ-9 in a clinical sample. Methods: 130 participants with mental health disorders were recruited during psychotherapeutic treatment in a mental health clinic. In a crossover design, they all completed the PHQ-9 in both the computerized and paper-and-pen versions in randomized order. Results: The internal consistency was comparable for the computer (α = 0.88) and paper versions (α = 0.89), and highly significant correlations were found between the formats (r = 0.92). PHQ-9 total scores were not significantly different between the paper and the computer delivered versions. There was a significant interaction effect between format and order of administration for the PHQ-9, indicating that the first administration delivered slightly higher scores. Limitations: In order to reduce the required effort for the participants, we did not ask them to fill out anything but the PHQ-9 once in paper and once in computer version. Conclusions: Our findings suggest that the PHQ-9 can be transferred to computerized use without affecting psychometric properties in a clinically meaningful way.