OBJECTIVE To identify actions taken by owners to socialize puppies < 20 weeks of age, to determine factors affecting attendance of structured puppy classes, and to examine associations between class attendance and owner response to various undesirable puppy behaviors. DESIGN Cross-sectional study. SAMPLE 296 puppy owners (each with 1 puppy). PROCEDURES Participants completed a survey at enrollment (to gather data regarding owner demographics and puppy characteristics) and again when puppies were 20 weeks of age (to gather information on socialization practices and owner responses to misbehavior and signs of fear in their puppy). Responses were compared between owners that did (attendees) and did not (nonattendees) report attending puppy classes. RESULTS 145 (49.0%) respondents reported attending puppy classes. Class structure differed greatly among respondents. Attendees exposed their puppies to a greater number of people and other dogs than nonattendees as well as to various noises and situations. Puppies of attendees were less likely than puppies of nonattendees to have signs of fear in response to noises such as thunder and vacuum cleaners as well as to crates. Fewer attendees reported use of punishment-based discipline techniques than did nonattendees. Almost one-third of puppies received only minimal exposure to people and dogs outside the home during the survey period. CONCLUSIONS AND CLINICAL RELEVANCE A notable number of puppies < 20 weeks of age in this study received few early socialization opportunities, which could lead to behavior problems and subsequent relinquishment. Opportunities exist for veterinarians to serve an important role in educating puppy owners about the importance of early puppy socialization and positive reward training.