context: gastroesophageal reflux disease is one of the most common digestive diseases and an important cause of distress to patients. diagnosis of this condition can require ambulatory ph monitoring. objectives: to determine the diagnostic yield of a wireless ambulatory ph monitoring system of 48-hours, recording to diagnose daily variability of abnormal esophageal acid exposure and its symptom association. methods: a total of 100 consecutive patients with persistent reflux symptoms underwent wireless ph capsule placement from 2004 to 2009. the wireless ph capsule was deployed 5 cm proximal to the squamocolumnar junction after lower esophageal sphincter was manometrically determined. the ph recordings over 48-h were obtained after uploading data to a computer from the receiver that recorded ph signals from the wireless ph capsule. the following parameters were analyzed: (1) percentual time of distal esophageal acid exposure; (2) symptom association probability related to acid reflux. the results between the first and the second day were compared, and the diagnostic yield reached when the second day monitoring was included. results: successful ph data over 48-h was obtained in 95% of patients. nearly one quarter of patients experienced symptoms ranging from a foreign body sensation to chest pain. forty-eight hours ph data analysis was statistically significant when compared to isolated analysis of day 1 and day 2. study on day 2 identified seven patients (30.4%) that would be missed if only day 1 was analyzed. three patients (18.7%) out of 16 patients with normal esophageal acid exposure on both days, showed positive symptom association probability, which generated an increase in diagnostic yield of 43.4%. conclusion: esophageal ph monitoring with wireless capsule is safe, well tolerated, does not require sedation. the extended 48-h period of study poses an increased yield to diagnose gastroesophageal reflux disease patients.