This study examined patient and appointment factors as predictors of nonattendance in addiction mental health services. Data were collected from the electronic files of 7,641 patients treated for a substance use disorder in outpatient clinics of an addiction mental health organization in the Netherlands. Negative binomial regression analyses revealed that cocaine use, poly substance use, limitations in interpersonal functioning, presence of anxiety disorder and cluster C personality disorder, age, level of education, source of income, and planning consistency were associated with nonattendance.