Background: Nomophobia, a state of socio-psychological illness, refers to a fear of lack of access to mobile phone, which is thought to be a modern age disorder that causes negative health risks and harmful psychological effects. This study aimed to determine the relationship between the smartphone use and nomophobia disorder among university students. Methods: The study utilized a cross-sectional method in which 320 students were selected via cluster sampling. Data collection tools included a nomophobia and smartphones use questionnaires. Data were analyzed using SPSS 22 software in two sections: descriptive statistics and inferential statistics. Results: The incidence rate of nomophobia among the students was moderate (3.1), and 73% of the students were moderate smartphone users. Nomophobia had a significant relationship with gender, age group, and level of education; and the frequency of using smartphones had a significant relationship with age group and level of education. There was a positive correlation coefficient between nomophobia and the frequency of using smartphones. The mobile phone use predicted nomophobia with a beta coefficient of 0.402 (P < 0.05). Conclusions: Given the incidence rate of nomophobia disorder was moderate, it is necessary to make preventive decisions and plan educational programs in this regard for the health of university students. Alternative actions are recommended for the treatment in low rate of nomophobia, but drug therapy should be used in more advanced stages; therefore, it is suggested that more attention to be paid to students' free time and entertainments. [ABSTRACT FROM AUTHOR]