Children with high-functioning autism (HFA) and attention deficit hyperactivity disorder (ADHD) often experience significant handwriting difficulties, which can hamper their academic progress and ability to express themselves through symbols and words. Handwriting of children with HFA was compared to those with ADHD based on performance on the speed subtest of the Handwriting Performance Test. Differences in handwriting speed, size and alignment of words, and proportion of handwriting errors, such as corrections and substitutions, were assessed between groups. Results indicated distinct profiles of handwriting problems in HFA and ADHD: children with HFA demonstrated poorer spatial arrangement of words and reduced handwriting speed, and those with ADHD made more handwriting errors, such as corrections and transpositions. These findings have important implications in understanding the similarities and differences for children with HFA and ADHD and lay the groundwork for effective intervention strategies.