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 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, higher HF correlated with greater ADHD symptomology (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; higher HF on the AHQ-D correlated with higher HF measured using a different HF scale (r(344)=0.69), as well as higher flow (r(345)=0.12) and higher mind wandering (r(345)=0.39) scores. Higher AHQ-D HF scores showed a weak negative correlation with less grit (r(345)=-0.29). Though lower HF weakly correlated with higher 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 symptomology. We suggest that the AHQ-D can be confidently used in future work as a valid way to measure HF in adults, both in general populations and in clinical cohorts.