This seemingly simple question is often overlooked by the novice. They simply take whatever the pet store says to them and consider it correct. Well, it may not be correct! Nine times out of ten when I am questioned by someone unable to breed Leopard geckos, it turns out they have two females. Females may 'cycle' and begin to produce eggs without a male present if conditions are right. This can lead the beginner to believe he or she is incapable of incubating eggs correctly, despite all attempts.
It can be very difficult to sex juvenile Leopard geckos accurately. Most often, they are sold as 'unsexed' meaning the breeder cannot tell, or as 'temperature sexed'. 'Temperature sexed' refers to geckos which hatched from eggs incubated at temperatures known to produce primarily a given sex. This is not a guarantee they will be sexed correctly, however. You still must mature them and verify the sexes visually.
Visual sexing cannot take place accurately until the gecko is about two-thirds grown, usually at about five months of age. This will vary a bit, based on individual growth rate.
A male Leopard Gecko
Here's a snapshot of the relevant parts of a mature male Leopard Gecko. Notice the well developed row of pre-anal pores, hi-lighted here in blue. Under magnification, these pores can be seen as open holes, often capped with a waxy build-up. Sexually mature specimens will exude a waxy substance from these pores which is smeared about the cage. This is a form of scent marking. Many beginners think their gecko is being cute 'wagging his butt all over the cage'. In reality, he is staking out his territory.
Do NOT put another male in with a mature male. They will fight violently, often to the death.
The real giveaway in males is the presence of the two enlarged 'hemipene bulges' at the base of the tail, hi-lighted here in red. If these are evident on your gecko, it is without doubt a male. Juveniles of both sexes will often show a bulge in this area, but it is not neatly divided in two as shown here.
A female Leopard Gecko
Here's a snapshot of the important parts of a mature female Leopard Gecko (Fig. 2). Many females will show poorly developed pits in the same location as the pre-anal pores of the male, or sometimes an enlarged row of scales, hi-lighted here in blue. Under magnification, these can be seen to be simple dents or pits in the scales, not true hollow pores, and they'll never have the waxy substance found on males. Many beginners mistake these for the pores of males. Many females also have very slight bulges in the same location as the 'hemipene bulges' as the male, hi-lighted here in red. However, they are never anywhere near as well-defined as those of a male.
It can be very difficult to accurately sex juveniles, ranging from impossible at birth to more and more educated guesses as they grow. Usually, the males will show with absolute certainty at around four months of age (if growing well). Note that this can vary a bit, and a specimen should not be considered female with certainty until about six to eight months of age, when any hope of it's being male can be ruled out safely. To sum up: if a young gecko is obviously male then OK, but if it's not obvious it could be either a female or a male waiting to finish developing. Years of experience sexing hundreds of juveniles each year is a definite plus....
