The diagnosis of Gardnerella vaginalis infection on the basis of microscopic and cultural findings was compared. A total of 340 specimens of vaginal secretion were Gram stained and plated on a medium selective for Gardnerella vaginalis. Positive culture was obtained in 165 cases. Microscopy was unequivocally positive in 95, doubtful in 58 and negative in 187. Positive microscopy was confirmed by culture in 99%. On the other hand, 21% of the negative microscopy results gave a false negative diagnosis. Specimens for which microscopy was doubtful were culture positive in 53% of the cases, including 12% with heavy growth. Thus, positive microscopy proved to be sufficient for a reliable diagnosis of Gardnerella vaginalis infection. However, in specimens with negative or doubtful microscopic findings, additional culture is recommended.