The purpose of this study was to develop a survey instrument to explore the conceptions that students hold after completing their first year of tertiary studies in quantum mechanics. The survey comprised four questions covering fundamental concepts: the photoelectric effect, the meaning of uncertainty, the nature of waves and the nature of energy levels. The instrument was administered to 231 physics students at the University of Sydney in 1995. A phenomenographic analysis was adopted and supported by content, context and correctness analyses. The results suggested that new concepts presented in class are considered superficially; reintegration of inappropriately associated pre-existing concepts does not frequently occur; development of mental models with time is minimal, the majority of students retain their original secondary school conceptions; and students have great difficulty in using models to interpret data.