In this paper we describe the development of a questionnaire designed to assess the probability content knowledge of prospective primary school teachers. Three components of mathematical knowledge for teaching and three different meanings of probability (classical, frequentist and subjective) are considered. The questionnaire content is based on curricular guidelines and primary school textbooks in Spain. The items were selected and adapted, after expert judgment, from previous research. The responses of 157 prospective primary school teachers were used to analyze the psychometric properties of the questionnaire and to provide information about various aspects of participants' probability content knowledge.