Choosing a dog
What is littermate syndrome?
Last updated 23 September 2026 · How we write and check this
Short answer
Littermate syndrome describes a pattern seen in puppies from the same litter, or unrelated puppies of similar age, raised together from a young age, where the two dogs become so bonded to each other that they struggle with individual confidence, separate training, and bonding fully with their human family. It is not a formal medical diagnosis but a recognized behavioral pattern many trainers and behaviorists actively try to help owners avoid.
What the pattern typically looks like
Affected puppy pairs often show intense distress when separated, even briefly, struggle to focus during individual training sessions because they are preoccupied with the other puppy, and sometimes develop an uneven dynamic where one puppy consistently dominates shared resources or attention. This can persist into adulthood if not addressed early.
Why it develops
Two puppies of similar age spend so much time together during a critical developmental window that they can end up more attuned to each other's signals than to human guidance, essentially becoming each other's primary source of security instead of gradually building that security with you. This is more likely when both puppies are left to interact constantly without deliberate separate time.
Preventing or managing it
If you do end up with two puppies close in age, deliberately separate them for individual training sessions, walks, and even crate time each day, so each puppy builds independent confidence and a direct bond with you rather than relying entirely on the other. Many trainers still recommend avoiding the situation altogether by spacing out when you bring puppies home.
Whether it affects every puppy pair
Not every pair of puppies raised together develops the full pattern, and some do go on to become well adjusted individually. The risk is simply higher than with a single puppy, which is why most professionals recommend avoiding the situation as a precaution rather than assuming it will not happen.
Key takeaways
- Littermate syndrome describes excessive mutual dependence between puppies raised together.
- Affected pairs often struggle with individual training, confidence, and separation.
- It develops when puppies rely on each other rather than building a bond with their owner.
- Deliberate separate time for training and walks helps prevent or manage the pattern.