In this paper the results of a systematic investigation into university students’ misunderstandings of d.c. simple circuit operations are reported. These results provide evidence of various misconceptions present before and after the teaching at university level of the topics on d.c. circuits: a battery as a source of constant current; the wrong interpretation of the junctional relation expressed by Ohm's law; power dissipated; resistors in parallel. In conclusion, a brief comment is made on the need to make university teachers aware of these results and on the many difficulties encountered in such an attempt.