The objective of the present study was to examine the relationship between sluggish cognitive tempo (SCT), subtypes of attention-deficit/hyperactivity disorder (ADHD), and anxiety disorders (AnxDs). One hundred and forty-one children (90 males, 51 females) aged 7–13 years were assigned to four groups, i.e., referred children with comorbid AnxDs and ADHD ( n  = 25), ADHD ( n  = 39), AnxDs ( n  = 41), and nonreferred controls ( n  = 36). Furthermore we explored the association between SCT and several neurocognitive measures (reaction time, verbal memory, and spatial memory). Diagnoses were established using Kiddie-SADS P/L. SCT was assessed using a 17-item mother-reported questionnaire. SCT correlated significantly with inattentiveness, regardless of the subtype of ADHD. Furthermore, we found significant differences in the levels of SCT among the four groups, with the highest SCT scores observed in the comorbid group. SCT correlated with variability in spatial memory; in contrast, there was no correlation between SCT and reaction time.