Hyperfocus (HF), or intense, deep concentration on a task, has gained significant research attention in recent years, particularly in regard to clinical populations such as Attention-Deficit/Hyperactivity Disorder (ADHD). The present work aims to provide validation of the 12-item dispositional adult hyperfocus questionnaire (AHQ-D) as a quantitative metric of HF in adults. We preregistered the study design and hypotheses. We administered the AHQ-D and several additional questionnaires to 347 adults (mean ± SD age: 33 ± 11 years; 47% female). Exploratory factor analysis revealed high factor loadings (0.57–0.81) on a single HF factor; item response theory analysis suggested that the questionnaire items had high discrimination and covered a wide range of responses; and we report strong internal consistency metrics (Cronbach’s alpha 0.93, mean split-half reliability 0.93). Replicating our previous work, HF was positively correlated with Conners’ Adult ADHD Rating Scale (CAARS) scores (r(345) = 0.53), suggesting that HF may be related to ADHD traits (though in this sample we did not specifically recruit individuals with ADHD). The AHQ-D demonstrated the hypothesized convergent validity; HF on the AHQ-D was positively correlated with HF measured using a different HF scale (r(344) = 0.69), as well as flow (r(345) = 0.12) and mind wandering (r(345) = 0.39) scores. AHQ-D HF scores showed a weak negative correlation with grit (r(345) = − 0.29). Though there was a weak negative correlation between HF and social desirability response tendency (r(345) = − 0.24), suggesting that those who care more about what others think may report less HF, there was no relationship between HF and extrasensory perception beliefs (r(345) = 0.01), suggesting that participants were not simply biased in their response tendencies. Taken together, we demonstrate strong scale metrics for the AHQ-D, the expected convergent validity, and a general lack of response bias, in addition to replicating our previous association of HF with ADHD traits. We suggest that the AHQ-D can be confidently used in future work as a valid way to measure HF in adults.