Benign paroxysmal positional vertigo (BPPV) is a common cause of vertigo, and has a typical constellation of physical findings. Atypical forms of paroxysmal positional nystagmus (APPN) also exist, and are thought to represent conditions which are in fact not 'benign'. We studied 100 consecutive patients with positional vertigo in order to learn whether APPN differed from classic BPPV in etiology or clinical fate, and to learn the incidence of central nervous system (CNS) disorders in these patients. APPN was present in 38% of these patients with diverse causes. One-fourth had CNS disorders or vascular insufficiency, the remainder, otogenic or idiopathic. APPN was more likely than BPPV to have a prolonged (persistent or recurring) clinical course. Although most cases eventually resolved, duration of symptoms tended to be longer, regardless of etiology. We conclude that APPN has a less favorable prognosis than typical BPPV, and that a CNS etiology should he suspected in prolonged cases.