Cast irons are known to be easy to shape by sand casting due to their high eutectic fraction. Despite this fact, together with cost benefits, obtaining good quality castings is not an easy task, although it depends on the level of defects allowed in each case. Casting defects are here reviewed and classified into three classes according to their known main origin: (1) related to the sand mixtures used to make the molds; (2) associated with the mold design and the geometry of the castings; (3) related to the casting alloy itself. The present work is an illustrated description of these defects, with details of their origin when well established, and of known remedies. In addition, an attempt has been made to clarify the possible cross-effects of the above three origins.