Objective: This study examined the relationship between attention-deficit hyperactivity disorder ((ADHD)) symptoms, smartphone addiction, and poor sleep quality in university students, and identified factors affecting ADHD symptoms. Participants: Data were collected from 197 students from March to June 2017. Methods: We adopted a descriptive cross-sectional study design. Results: ADHD symptoms were positively correlated with smartphone addiction (r = 0.424, p < 0.01) and poor sleep quality (r = 0.313, p < 0.01). The regression analysis showed that academic achievement ([beta] =0.128, p = 0.038), smartphone addiction ([beta] =0.327, p < 0.001), sleep disturbance ([beta] = 0.197, p = 0.003), and daytime dysfunction ([beta] = 0.269, p < 0.001) were identified as factors significantly influencing ADHD symptoms, accounting for 31.1% of their variance. Conclusions: Interventions for university students with ADHD symptoms should involve the evaluation of these four factors as a multifaceted approach to reducing ADHD symptoms.