Disturbances of mood in young people encompass a wide range of clinical phenomena and associated risk factors. Similarities in the syndromic expression of depression in juveniles and adults are well documented, but homogeneity of phenotype does not mean there is a single common disorder across all age groups. An unusually high density of familial illness appears to be a distinguishing feature of juvenile-onset mood disorders. Parental matings involving depression and anxiety appear significantly to increase liability for both conditions in offspring, whereas parental alcoholism elevates risk to offspring of conduct problems and substance abuse. Depression is clearly among the most prominent types of psychopathology in offspring of parents with affective disorder, unipolar major depression in particular. However, psychopathology in general is widespread in these samples, thus raising questions about the mechanisms underlying parent-child resemblance for depression and the co-aggregation of affective and nonaffective conditions.