White coat, dark-room problem, clear rule
A young West Highland White Terrier is male if a raised rounded opening sits on his belly, and female if her opening is a slit immediately beneath her tail. The Westie's brilliant white double coat reflects light back at you and erases contrast, which makes this breed's check more about lighting and parting hair than about anatomy. Boldness, digging enthusiasm, and that trademark terrier self-confidence appear in both sexes in full measure. Set the puppy where you can see skin against a darker towel, part the belly coat deliberately, and the spacing between the openings resolves the question cleanly.
Setting up a Westie-sized inspection
Wait for the lull after a garden patrol and a meal, then settle your young West Highland White Terrier across your lap on a dark blanket that gives the white coat something to contrast against. Westies are built low and sturdy, and a puppy will brace all four feet if it feels tipped, so roll it only partway onto one side with its back resting against your arm. Part the harsh outer belly coat and the softer undercoat beneath it with your fingers, working down to pink skin. A helper keeping a steady hand on the puppy's chest prevents the sudden terrier twist that ends most first attempts.
Identifying a male Westie puppy
On a male West Highland White Terrier, the parted belly coat reveals a small hooded bump with a central tiny opening, set along the midline well in front of the rear opening. In white-coated puppies that bump can cast the only shadow on the whole underside, which actually helps you spot it. Behind it, near his anus, a young male's testicles may be two subtle peas under the skin or nothing you can detect yet, and either finding fits a normal male puppy. What settles his sex is the belly bump and the clear runway of skin between it and his tail end.
Identifying a female Westie puppy
On a female West Highland White Terrier, part the belly coat from chest to tail and you will find only the flat little navel scar, with the skin otherwise smooth beneath the white layers. Her genital opening sits under her tail as a small vertical slit just below her anus, often fringed by coat that needs sweeping aside. Viewed against that dark blanket, the close pairing of her two openings becomes readable even through Westie brightness. If the belly is empty of any raised structure and the slit hugs the anus, your Westie puppy is female, whatever her swagger suggests.
Westie confidence proves absolutely nothing
Young West Highland White Terriers are earthdog terriers to the core in both sexes: females charge tunnels, thrash toys, and rule the litter, while males can be every bit as theatrical about a thorn in a paw. Owners who sex puppies by attitude in this breed are wrong roughly half the time and surprised every time. The navel scar is the other reliable trap, sitting flat and slightly higher than a true male bump but catching lamplight in a way that flatters it. Daylight, a parted coat, and a dark background underneath remove both traps at once.
Recording the result before the first outing
Have the veterinarian confirm your West Highland White Terrier's sex at the first puppy appointment if glare and coat left you guessing, and book sooner for any swelling, discharge, sore skin under the tail, or straining to pass urine. Westies are prone to sensitive skin generally, so changes around either opening deserve a professional look rather than home experimentation. With the sex settled, entering it in KinsLe Pet Passport bundles the answer with this Westie's portable record packet for appointments, boarding, and journeys ahead.