Sleep disturbances are common in many progressive metabolic encephalopathies. The possible presence of disturbed sleep–wake behaviour in the lysosomal storage disorder aspartylglucosaminuria, has not been previously studied, however. The sleep–wake behaviour of 81 patients with aspartylglucosaminuria (AGU, age 3–55 years, median 22 years; 42 female and 39 male) and 49 controls (age 2–57 years, median 18 years; 25 female and 24 male) was assessed through a postal survey. A slightly modified version of the validated Basic Nordic Sleep Questionnaire was used. Fifty-eight per cent of the AGU patients were reported to suffer daily from a sleep-related problem (controls 31%, p < 0.01). In AGU adults (age >17 years) and children (age ≤17 years), the corresponding figures were 52% and 61%, respectively (control children 22%, p < 0.05 and control adults 38%, p = 0.06). In AGU children, settling difficulties were reported to occur significantly more commonly than in control children. Children with AGU were also reported to snore more often than were the controls. Adults with this disorder were found to suffer from severely fragmented night-time sleep, which was experienced as highly distressing by the parents and other caregivers. A long night sleep period was reported to be common in the ageing AGU patients (AGU 9.5 ± 1.7 vs controls 7.2 ± 1.0 h, mean ± SD, p < 0.001). Parents and caregivers also often complained about disturbing movements during sleep in AGU patients. In conclusion, both children and adults with aspartylglucosaminuria were reported to display several types of sleep disturbances significantly more commonly than healthy controls.