Negative symptoms in schizophrenia may be classified as primary or secondary. Primary negative symptoms are thought to be intrinsic to schizophrenia, while secondary negative symptoms are caused by positive symptoms, depression, medication side-effects, social deprivation or substance abuse. Most of the research on secondary negative symptoms has aimed at ruling them out in order to isolate primary negative symptoms. However, secondary negative symptoms are common and can have a major impact on patient-relevant outcomes. Therefore, the assessment and treatment of secondary negative symptoms are clinically relevant. Furthermore, understanding the mechanisms underlying secondary negative symptoms can contribute to an integrated model of negative symptoms. In this review we provide an overview of concepts, evidence, assessment and treatment for the major causes of secondary negative symptoms. We also summarize neuroimaging research relevant to secondary negative symptoms. We emphasize the relevance of recent developments in psychopathological assessment of negative symptoms, such as the distinction between amotivation and diminished expression, which have only rarely been applied in research on secondary negative symptoms.