Prefrontal cortex in frontal lobe (FL) is the center of executive functions (EF). FL damage can lead to executive dysfunction by influencing frontal-subcortical circuits (dorsolateral, orbitofrontal, ventromedial). Damage to the dorsolateral prefrontal cortex (DLPFC) can lead to deterioration in EF, whereas damage to the orbitofrontal cortex (OFC) can lead to personality changes with the characteristic of disinhibition and irritability. In addition, damage to the anterior cingulate cortex/medial prefrontal cortex (ACC/MPFC) can result in decreased spontaneity. Neuropsychological tests are important components in the assessment of EF including goal-directed behavior, decision-making, risk assessment, making plans for the future, setting of priorities and order of our actions. Clinical conditions affecting frontal-subcortical connections outside of the FL can also lead to executive dysfunctions and frontal lobe syndrome (FLS). This case report is about an adolescent patient diagnosed as FLS. The clinical symptoms, assessment and treatment processes of this case are discussed in this report. The case is a 15-year-old boy that was admitted to our clinic with behavioral problems, which began after a car accident three years ago. Magnetic resonance imaging (MRI) of the brain indicated hyperintense signal increase in periventricular deep white matter that is associated with traumatic brain damage. Neuropsychological tests results (Stroop, Wisconsin Card Sorting Test, Serial Digit Learning Test, Line Orientation Test, Verbal Memory Processes Scale) have demonstrated impairment in cognitive flexibility, verbal fluency, setting priority, inappropriate response inhibition, sustained attention, planning, problem solving, organization skills and subcortical memory functions. We thought that cognitive and behavioral symptoms of this case were associated with the dysfunctions of frontal-subcortical circuits, independent of an obvious frontal lesion. FLS for the patients with sudden-onset behavioral and cognitive problems after head traumas should be kept in mind in differential diagnosis, even in the absence of an obvious frontal lesion.