In this paper, 2 patients, a daughter with periodic alternating nystagmus and a mother with congenital fixation nystagmus, are presented, and the similarities of the two disorders are discussed, not only in the eye movements, but also in their underlying abnormalities. The literature was reviewed, and the link between periodic alternating and congenital fixation nystagmus, which had been suggested based on circumstantial evidence, may be confirmed by our cases. The possible evidence of inheritance suggests that the two disorders share common abnormalities in visual processing.