This book, first published in 1887, is based on lectures given by Dr Langdon Down, a physician renowned for his work with mentally handicapped children at a time when there was very little interest in them. The book is well-known, because it contains the original description of the common syndrome of 'mongolism', now universally called Down syndrome. It is, however, far more than a mere description of Down syndrome; it contains a great deal of material about mental disorders in childhood that is as relevant today as it was a hundred years ago.