Perioperative medication errors are preventable complications that if allowed to occur can result in undesirable and even catastrophic outcomes for the patient. Perioperative drug errors are poorly reported in our country but they can be a tool for assessment of quality of care to patients undergoing surgery. Drug errors result from system errors like poor labeling and identification, sound alike and look-alike medications, wrong doses and omission to administer a drug. This chapter covers the responsibility to the patient, background for the occurrence of drug errors, incidence and classification of drug errors, pattern of medication errors, look-alike, sound-alike (LASA) and similar packaging, error prevention in theater setting, medication errors in the ICU, and management of errors in Operation Theater and ICU.