Clinically significant false-positive human chorionic gonadotropin (hCG) test results are rare. However, some individuals have circulating factors in their serum (eg, heterophilic antibodies or nonactive forms of hCG) that interact with the hCG antibody and cause unusual or unexpected test results. False-positive and false-negative test results can occur with any specimen, and caution should be exercised when clinical findings and laboratory results are discordant. Methods to rule out the presence of interfering substances include using a urine test, rerunning the assay with serial dilutions of serum, preabsorbing serum, and using another assay. Physicians must decide whether the risks of waiting for confirmation of results outweigh the risks of failing to take immediate medical action. Patients should be notified if they are at risk for recurrent false-positive hCG test results, and this information should be included in the patient's medical record.