Internet-based interventions (IBIs) to treat psychological disorders are available, but accessibility to these to treat attention-deficit/hyperactivity disorder (ADHD) in young adult populations is quite limited. The current study examined the feasibility of a proposed IBI for ADHD and participant perceptions regarding treatment acceptability and credibility, and outcome expectancy. Participants (N = 235; aged 18–35) with a prior ADHD diagnosis were recruited through Amazon’s Mechanical Turk (MTurk) and were provided with a proposed IBI and explanatory outlines of treatment module content. Participants in the cross-sectional study were randomly assigned to either a tailored (i.e., targeted content modules), minimal (i.e., presented overall fewer and non-targeted modules), or full (i.e., all possible modules) condition. Results demonstrated moderate IBI acceptability among participants in the tailored and full conditions. The majority of participants preferred IBI over face-to-face (F2F) treatment, and most individuals who preferred F2F treatment also considered an IBI to be an acceptable treatment modality. Lack of significant mean differences between the tailored and full conditions on several of the main outcomes of interest (e.g., perceptions of acceptability) suggests that implementation of either method of treatment could prove effective. Differences based on treatment length and relevance, and biological sex were also explored. Implications, limitations, and future directions are discussed.