The easiest way to sex a leopard gecko is to look for the presence of hemipenal bulges and preanal pores. If these features are present, the animal is a male.
To sex a leopard gecko, hold the animal belly-up and look at the area around its vent. A male leopard gecko has a row of preanal pores in a V-shape just in front of the vent. Male leopard geckos mark territory using a waxy substance extruded from these preanal pores. Male geckos also have a noticeable bulge behind the vent, which signifies the presence of the hemipenes, the male reproductive organ. Female geckos may have visible pores in front of the vent, but these are not as noticeable as a male's. Sexing a gecko is most reliable once the animal is over 6 months old. When compared side-by-side, male geckos tend to be stockier than females and have wider heads, but this is an unreliable method for sexing leopard geckos. Accurately sexing leopard geckos is important when housing multiple animals, because male geckos often fight, and this may result in injuries.
When breeding leopard geckos, the sex of the offspring is dependent on temperature. Lower temperatures, in the range of 79 to 81 degrees Fahrenheit, produce mostly females, while incubating temperatures between 88 and 91 degrees Fahrenheit yield mostly males. A relatively even number of males and females results from a temperature range of 85 to 87 degrees Fahrenheit.