Instructions
Wait until your iguana is a year old, when the sexual organs become visible. If you are unaware of your iguana's age, check its length. An iguana that is a year old is typically between eight and nine inches long from snout to vent. The vent is the opening located at the base of the iguana's tail.
Check for male reproductive organs. The male's hemipenal bulge will start to become visible after the iguana is one year old and is located at the iguana's vent. A female iguana will have no bulge at her vent.
Check for behavioral differences in your iguana after it is a year old. Male iguanas may become more aggressive as they become older, and some may become unable to live cooperatively with other iguanas. Male iguanas will start to bob their heads up and down more, and they may even follow their owners around in a stalking manner.
Check your iguana's head. A male iguana will have lower jowls that are more massive than a female's jowls. A female's head is more slender and narrow, while a male's head is large and bulky.
How to Know if Iguanas Are Males or Females
Telling the difference between male and female iguanas is difficult when the reptiles are younger than a year old, but once they reach sexual maturity, the differences will become more apparent. Male and female iguanas will differ in size and and attitude as they get older, so it is best to try and sex an iguana after it has achieved maturity.