This chapter on hidden impairments considers the neurodevelopmental disorders including autism spectrum disorders and attention deficit hyperactivity disorder and their impact on employment and how occupational health (OH) professionals can provide appropriate advice on fitness to work. These chronic disorders have a combined prevalence of up to 6%, are highly co-morbid, and commonly present with specific learning disabilities such as dyspraxia, dyslexia, and dyscalculia. As the term implies, they are often missed by clinicians and are costly to society. With equality legislation and increasing diagnosis of neurodevelopmental disorders, OH professionals should be aware of the functional impact of these conditions and the behavioural and cognitive challenges to performance at work so they can best support the individual and advise the employer. The chapter provides guidance on how work can be designed and organized to enable people with neurodevelopmental disorders to obtain and retain suitable employment and to benefit from work.