The study examined the impact of two grammatical factors on marking Hebrew adjectives in agreement with plural nouns in adults with attention-deficit hyperactivity disorder (ADHD) compared with peers without ADHD. Participants were 36 adult speakers of Hebrew, who were administered a judgment test of 144 sentences, each containing an adjective in agreement with a plural noun in one of three different syntactic configurations-predicative adjectives, attributive adjectives in sentence-initial position, and attributive adjectives in sentence-final position. Noun suffixes were regular, semiregular (ambiguous), and irregular. Findings showed that participants with ADHD displayed lower accuracy and longer response time compared with controls. As morphological and morpho-syntactic difficulty simultaneously increased, participants with ADHD were significantly more likely to perform less well compared with controls on both accuracy and speed. These findings indicate that adults with ADHD might be suffering from a linguistic impairment exacerbated under more cognitively and linguistically demanding conditions.