A predictive technique for treating diabetes mellitus is described whereby a patient's blood glucose levels are monitored "continuously" over an extended period of time and a life-event diary is maintained records all significant life-events (e.g., food intake, medication, exercise, mood/emotions, etc.). This information is analyzed to derive a mathematical model that closely matches the patient's glucose level variations for the period of monitoring. Specific daily time periods of dysglycemic vulnerability are determined by calculating when the mathematical model predicts that crossings of predetermined hyperglycemic and hypoglycemic threshold levels will occur. These predicted periods of vulnerability are then used to devise a therapeutic plan that administers treatment in anticipation of predicted dysglycemic excursions, thereby limiting the extent of those excursions or eliminating them altogether.