The Sealyham Terrier is a healthy breed, with relatively few genetic anomalies compared to other breeds. A survey conducted by the ASTC in 2001 showed lens luxation and allergies to be the most prevalent disorders. Lens luxation is a disease common in many terriers. The lens of the eye becomes detached from the outer wall of the eye. It nearly always affects both eyes, although usually not at the same time. Recurring bladder infections and allergy-related ear infections were also concerns. Disk problems occur occasionally. Despite some dog books citing deafness in the breed, it does not seem to be widespread. All of these problems can be managed with proper veterinary care and are not life-threatening. It is always important to choose a reputable breeder who monitors the health of their puppies throughout their lives and has tried to eliminate genetic diseases through selective breeding.

The ASTC is a "Founder" Donor to the Canine Health Foundation, donating $10,000, and is participating in allergy and lens luxation research projects to try to find genetic markers and possibly genetic tests to use as one of many factors affecting breeding decisions.

The ASTC, in collaboration with the Institute for Genetic Disease Control has founded the S.I.G.H.T. Registry (Sealyham Eye Genetic Health Tracking), an open registry in which Sealyham Terrier owners can register current eye exams, pedigrees and other pertinent information about their dogs. The information is available to registered users of the database and can be used to make informed breeding decisions.

GDC and the SIGHT Registry are presently conducting a survey among Sealyham owners world-wide to determine the prevalence of lens luxation and other eye diseases.

The ASTC is dedicated to keeping our Sealyham a healthy dog and to address the few diseases which do affect our lovely breed.