In the last ten to fifteen years refinements in the registration techniques for ocular movements have allowed a more precise definition of nystagmus forms and have thus brought new insight into their pathophysiology. As a result we can distinguish four types of disturbances of the subsystem for the slow movements, which are fundamental to nystagmus. This and other discoveries also have consequences for the practical diagnostics of neuro-ophthalmological diseases. In this article, with the help of a simple practical scheme, extra attention will be given to the clinically relevant new information needed to make the diagnosis or differential diagnosis of conditions in which nystagmus is one of the most important signs.