Over the course of studying attention-deficit/hyperactivity disorder (ADHD), the concept of sluggish cognitive tempo (SCT) has surfaced. SCT reflects confusion, sluggishness, and decreased alertness and activity. Research on the relationships among SCT, ADHD, and other psychopathologies has been mixed. Several studies have demonstrated the independence of SCT, but the close relationship it appears to have with inattention and internalizing symptoms makes it challenging to maintain that SCT is a discrete disorder. The current study adds to the literature on ADHD and SCT by examining differences among children with ADHD + SCT, ADHD Only, and SCT Only. Groups were compared on measures of demographic variables, co-occurring symptomatology and comorbid diagnoses, neuropsychological functioning, and academic achievement. Analyses revealed that those with SCT were often older. Additionally, parent report suggested that those with SCT exhibited more symptoms in domains such as internalizing problems, externalizing problems, sleep problems, and social withdrawal. In contrast, few differences were found for teacher report, and the trends departed from parent report indicating that those with ADHD had higher levels of attention problems, internalizing problems, externalizing problems and social problems. On neuropsychological tests, those with SCT Only generally appeared less neuropsychologically-impaired than those with ADHD. Regression analyses involving multiple covariates revealed that SCT symptoms were still uniquely related to social withdrawal, but surprisingly, were positively related to academic achievement scores. Overall, the findings from this study echo the conception that SCT symptoms contribute to the clinical picture in ways that are important to consider. In particular, SCT symptoms appear to have associations with internalizing problems, more specifically social withdrawal, and sleep problems. Given the limited evidence for neuropsychological impairment in those with SCT Only, treatments for SCT may involve elements designed to address anxiety/depression, sleep, and social withdrawal rather than neuropsychological impairments.