Human immunodeficiency virus (HIV) is increasing in Thai youth. Consequently, a school-based National Condom Strategy program was launched in 2015 to reduce the rate of HIV and sexually transmitted infections. We conducted in-depth interviews of 31 parents/adoptive guardians of high-school age Thai boys to explore parents' knowledge, attitudes, behaviors, and barriers to promoting condom use and its role in preventing HIV/sexually transmitted infections. A descriptive phenomenological approach and thematic analysis was used. Most participants had knowledge and positive attitudes about condom use. Half disagreed with the National Condom Strategy of placing condom vending machines in schools. More than half did not initiate teaching male youth about condom use until the youth had broached the question or only intended to do so when the youths were older. Barriers included parents' lack of condom experience and knowledge, embarrassment/discomfort when talking about condoms, and belief that youth were not sexually active. Parents are a key factor for supporting condom use in Thailand. This study supports the need for education programs for parents.