Objectives: This study investigated the Wechsler Adult Intelligence Scale-Fourth Edition Letter-Number Sequencing (LNS) subtest as an embedded performance validity indicator among adults undergoing an attention-deficit/hyperactivity disorder (ADHD) evaluation, and its potential incremental value over Reliable Digit Span (RDS). Method: This cross-sectional study comprised 543 adults who underwent neuropsychological evaluation for ADHD. Patients were divided into valid (n = 480) and invalid (n =…