Despite the significant growth and capabilities of mobile technologies, there is limited empirical evidence on teachers' perceived mobile technology-learning barriers. This study investigated Greek teachers' perceptions of barriers to using mobile technology in school classrooms. A 28-item questionnaire was administered to 557 teachers and six barrier-factors were extracted: 'lack of resources', 'lack of support', 'lack of time', 'lack of teacher confidence', 'class conditions' and 'concerns about students'. The questionnaire was a valid and reliable tool for the investigation of various dimensions of teachers' perceived barriers. Gender, school level, age and ICT training had significant but small effects on specific barrier-factors. The order of importance of barrier-factors was similar for users and non-users ('lack of resources', 'support' and 'class conditions') independently of the type of mobile device used in class. 'Concerns about students' was identified as a major barrier only by non-users. Implications for educational policy and professional training are discussed.