Two hundred forty-two patients referred for various gastrointestinal complaints were evaluated for clinical parameters that would predict findings of lactose malabsorption. Breath hydrogen and blood glucose lactose tests were performed after ingestion of 50 g lactose. Presenting complaints, duration of symptoms, and patient demographics such as age, sex, and ethnic heritage were not different between lactose malabsorbers and absorbers as defined by the breath hydrogen lactose test. Food-related symptoms in general and after specific foods such as milk, ice cream, cheese, and yogurt were also similar between groups. Prior to testing, 30% of malabsorbers (N = 161) and 36% of absorbers (N = 81) reported lactose-related symptoms (P = NS). The blood glucose response to lactose was abnormal in 60% of malabsorbers and 15% of absorbers. This study confirmed our impression that it is difficult to predict lactose absorption status by clinical parameters. The majority of our lactose malabsorber patients were unaware of lactose-associated symptoms. Furthermore, symptom assessment, demographics, food history, and blood glucose testing did not predict abnormal hydrogen responses to lactose.