Previous studies have shown that hoarding behavior usually starts at a subclinical level in early adolescence and gradually worsens; however, a limited number of studies have examined the prevalence of hoarding behavior and its association with developmental disorders in young adults. The aims of this study were to estimate the prevalence of hoarding behavior and to identify correlations between hoarding behavior and developmental disorder traits in university students. The study participants included 801 university students (616 men, 185 women) who completed questionnaires (ASRS: Adult ADHD Self-Report Scale version 1.1, AQ16: Autism-Spectrum Quotient with 16 items, and CIR: Clutter Image Rating). Among 801 participants, 27 (3.4%) exceeded the CIR cut-off score. Moreover, the participants with hoarding behavior had a significantly higher percentage of ADHD traits compared to participants without hoarding behavior (HB(+) vs HB(−), 40.7% vs 21.7%). In addition, 7.4% of HB(+) participants had autism spectrum disorder (ASD) traits, compared to 4.1% of HB(−) participants. A correlation analysis revealed that the CIR composite score had a stronger correlation with the ASRS inattentive score than with the hyperactivity/impulsivity score (CIR composite vs ASRS IA, r = 0.283; CIR composite vs ASRS H/I, r = 0.147). The results showed a high prevalence of ADHD traits in the university students with hoarding behavior. Moreover, we found that the hoarding behavior was more strongly correlated with inattentive symptoms rather than with hyperactivity/impulsivity symptoms. Our results support the concept of a common pathophysiology behind hoarding behavior and ADHD in young adults.