The Casoni test is a skin test used in the diagnosis of hydatid disease. The test involves the intradermal injection of 0.25 ml of sterilised fluid from hydatid cysts/human cyst and sterilised by Seitz filtration on forearm and equal volume of saline injected on the other forearm. Observations made for next 30 mins and after 1 to 2 days.^[1] A wheal response occurring at the injection site within 20 minutes is considered positive (immediate hypersensitivity). Delayed hypersensitivity reactions usually read after 18–24 hours.^[2] The test is positive in about 90% of cases of hydatid disease affecting the liver, but positive in less than 50% of patients with hydatid disease elsewhere in the body; false positive results are also common. Being a type I hypersensitivity reaction, anaphylactic reaction tray must be kept ready before carrying out the test.^[3] Consequently, serological tests are now generally used.^[4] The test was described in 1912 by Tomaso Casoni.^[5]