Primary method:  The best way to distinguish between male and female is by looking under the tail below the vent.  Males are usually first sexable by the appearance of hemipenal bulges, as pictured below. The male hemipenal bulges appear as two pads on either side where the hemipenes are stored, and females will have just one bump in the center.  Males are more likely to be inaccurately sexed as females, especially if they are slow to mature.  Most babies have female characteristics and the difference will not be apparent until at least several months of age, possibly much longer, and even up to a year.  The visual difference here may never be as dramatic as in other species, such as bearded dragons. 

    Secondary methods:  Males also have bigger, boxier heads, larger jowls, thicker tails, wider vents, longer frills, larger femoral pores that can excrete a waxy substance as adults, and are reported to have brighter colors on average.  Based on personal observation - New Guinea males often have solid dark grey to black frills with yellow flecking and females retain a more mottled pattern throughout the frill and body.  There is much variation within both sexes.

    Females are slightly smaller and much leaner, and tend to be a little more skittish on average as well.  At full growth, they may only reach approximately half the weight of a healthy male.  Adult New Guinea females should weigh approximately 200-250 grams, and males should weigh at least 400, even up to 600 grams, depending on age and individual variation.  "Adult" weight is usually achieved by 2-3 years of age.

    

    Both sexes generally have good attitudes at adults especially if they were captive born/bred, although males may be more likely to tolerate handling.  Females tend to have a more "independent" attitude.  They usually don't mind being gently picked up while inside the enclosure, but they may not remain calm if carried out.  The females especially do however seem to enjoy being able to free-roam and explore.  Males are often more calm initially when being handled, but may at any point abruptly decide they've had enough and take off.  Experiences may vary greatly.

    

    Many people prefer males are pets because of the more impressive physical appearance and to avoid any complications females can get with infertile egg-laying.  However, adult males can be very territorial and may frill & hiss at their owners.  Males are also more prone to sulking behavior, where they go through phases of low activity & appetite in response to a change in environment or other unknown cause that for some reason upsets them.  Many females that are skittish as juveniles turn out to be very calm and personable as they mature into adults.  Females can be housed together, if given adequate additional space.  Males should be housed alone or with any number of females, given that they can coexist without continual harassment, which is not always the case.  Some males may provide undue stress and/or injuries to a female resident, and may require separation.

Visuals:

Adult Female (1 bump)

Adult Male (2 bumps)