Post-headshake nystagmus (PHN) has recently been described as a clinically useful physical sign implying uncompensated asymmetric input from the vestibular end organs. A rapid 20-second headshake and sudden stop produces a jerk nystagmus of 5- to 20-second duration in certain individuals with symptoms suggestive of a peripheral vestibulopathy. This retrospective review of 214 patient evaluations was undertaken to study the associations between post-headshake nystagmus, caloric deficits after bithermal binaural irrigation, and the presence of vertigo. Both clinical observation of the nystagmus with eyes open (PHN-OBS) and routine EOG recording with eyes closed (PHN-EOG) were used. In patients with unilateral caloric deficits, 42% (18 of 43) had PHN-EOG, compared with 18% (3 of 17) in patients with bilateral dysfunction and 15% (23 of 154) in patients with normal calorics (p < 0.001). In similar fashion, 26% (32 of 124) of patients with vertigo (recent or past) had PHN-EOG compared to 13% (12 of 90) of patients without vertigo (p < 0.03). Finally, of 110 cases with both PHN-EOG and PHN-OBS performed, 45% (9 of 20) with PHN-EOG also had PHN-OBS, as opposed to only 4% (4 of 90) without PHN-EOG displaying PHN-OBS (p < 0.0001). We conclude that the prevalence of post-headshake nystagmus is increased in patients with either a unilateral caloric deficit or a history of true vertigo, and is best detected in the absence of vision.