<p>Despite the numerous advantages brought about by the rapid development of technology, it can also lead to many psychological issues that threaten human health, such as fear of missing out (FOMO) and problematic smartphone use (PSU). The present study, inspired by the Cognitive-Behavioral Models of Obsessive-Compulsive Disorder (OCD), likens FOMO to the anxiety that accompanies obsessions, and PSU to the compulsive behaviors exhibited to alleviate this anxiety. Additionally, it is assumed that cognitive distortions and metacognitions are seen in the literature to be related to OCD and problematic technology use, may also play a role in the FOMO-PSU relationship. From a cognitive-behavioral approach, the present study, assuming that FOMO represents negative emotion and PSU represents negative behavior, also considers that cognitive distortions and metacognitive beliefs act as mediators in the FOMO-PSU relationship, suggesting maladaptive thought patterns contribute to excessive smartphone use. A total of 386 individuals aged 18–36 participated in the study. The measurement tools of the present study are the Demographic Form, Fear of Missing Out Scale, Cognitive Distortion Scale, Metacognitions Questionnaire-30, and Problematic Mobile Phone Use Scale. According to the findings, cognitive distortions and metacognitions have a partial mediating effect on the relationship between FOMO and PSU. Additionally, the hopelessness subscale of cognitive distortions and the cognitive confidence subscale of metacognitions also play a partial mediating role in the relationship between FOMO and PSU. In conclusion, mental processes such as cognitive distortions and pathologic metacognitive beliefs are effective in exacerbating the impact of FOMO on PSU.</p>