OBJECTIVE To report a case of medication dispensing error by administration of similarly packaged drugs. CASE SUMMARY A 6-year-old East Indian boy with asthma was mistakenly given alendronate, a bisphosphonate, for 3 months instead of montelukast, a leukotriene-receptor antagonist. Symptoms of esophageal irritation developed and disappeared on discontinuation of alendronate. DISCUSSION Alendronate and montelukast have very similar packaging and are available in dosages that also can be similar for some patients. Alendronate caused symptoms of irritative gastritis in this child before the error was identified. This case report emphasizes one of the possible sources of medication dispensing errors: a mistaken identification due to similar packaging (confirmation bias). Manufacturers can help to prevent medication errors in many ways; in this case, more distinct packaging would have decreased the risk of error. A standard bar-coding scheme among manufacturers could lead to an important improvement in the safety of medication dispensation. Practitioners are also encouraged to report such errors to the United States Pharmacopoeia Medication Errors Reporting Program. CONCLUSIONS With increased awareness of medication errors, healthcare practitioners, manufacturers, and patients should take precautionary steps to prevent dispensing errors and their consequences.