Alcohol misuse is a common mental disorder that can have devastating effects on an individual’s physical and mental health. Although alcohol misuse is both prevalent and disabling, only 21% of individuals receive treatment. Internet-delivered cognitive behaviour therapy (ICBT) may serve as a promising solution for the treatment gap, as it minimizes concerns about the stigma surrounding seeking treatment. Previous studies in alcohol treatment literature address a phenomenon named Assessment Reactivity (AR) which suggests that assessment interviews are predictive of significant changes in pre-treatment drinking. This may be of clinical importance as early abstinence from alcohol has been significantly associated with longer periods of continuous abstinence. The primary objective of the current study was to explore pre-treatment change by experimentally manipulating assessment in an ICBT program for alcohol misuse. As such, 87 clients were randomly assigned to receive an assessment interview or no assessment interview prior to beginning treatment. It was hypothesized that clients who received an assessment interview would experience greater reductions in alcohol consumption and depression, as well as increased motivation to improve their drinking behaviours. Results indicated that there were no significant differences in drinking behaviours between groups at pre-treatment. However, significant reductions in alcohol consumption were observed amongst both groups, suggesting that factors other than an assessment interview may contribute to client’s willingness to improve their drinking behaviours. No significant differences in motivation to change or depressive symptoms were observed between groups, although, both groups experienced a significant increase in motivation and decrease in depressive symptoms over time. The results have valuable implications for the delivery of ICBT in routine care.