AIM: To compare the posture-induced variations in intraocular pressure (IOP) between the primary open angle glaucoma (POAG) and non-glaucomatous eyes. METHODS: A case-controlled age matched study was conducted in 55 successive newly diagnosed POAG and 56 non-glaucomatous patients seen in glaucoma clinic and general outpatient eye clinic in the Alex Ekwueme University Teaching Hospital, Abakaliki. The IOPs of eligible correspondents were measured with Perkin's hand-held tonometer in the sitting, supine flat and supine with pillow positions respectively. Measurement of IOP in each position was done after 15min of assuming such posture. RESULTS: The IOP difference between the sitting and supine flat position was significantly higher in the POAG than non-glaucoma subjects (7.68±2.08 vs 4.03±0.13 mm Hg, P<0.001). The IOP difference between the sitting and supine with pillow positions was 2.61±1.49 mm Hg for POAG and 1.44±0.70 mm Hg in non-glaucoma (P<0.001), while difference between supine flat and supine with pillow positions was 5.07±2.24 mm Hg in POAG and 2.59±0.66 mm Hg in non-glaucomatous patients (P<0.001). CONCLUSION: Greater variations in posture induced IOP occurred in POAG patients than non-glaucomatous. The posture induced IOP variation is lowest in the sitting position and highest in the supine flat position. Evaluation of posture induced IOP changes may be an important tool in the management of glaucoma.