Lesch–Nyhan syndrome (LNS) is a rare disorder of metabolism caused by a defective gene on the X chromosome. It is typically characterized by choreoathetosis, hypertonia, hyperreflexia, and self-mutilation. The present study is a 4-year follow-up investigation of the cognitive status of six subjects with a mean age of 17 years 10 months (range 14 years 9 months to 23 years). The Stanford–Binet Intelligence Scale: IV was used. Each of the four domains assessed by this battery (verbal reasoning, abstract/visual reasoning, quantitative, and short-term memory) was compared with previous findings of the same subjects at their initial test and 2-year follow up; the aim being to gain further insight into the clinical course of LNS over time. The results suggest that while the subjects generally continued to acquire new information and skills over time, their standardized scores declined, indicating that a plateau was reached in their skill levels relative to their peers, as also seen in other developmental disabilities. Deficits were noted in working memory, particularly on tasks that involve considering multiple features simultaneously.