Background Child maltreatment is a potent risk factor for psychopathology. Although the developmental timing of first exposure to maltreatment is considered important in shaping risk of future psychopathology, no consensus exists on whether earlier or later exposures are more deleterious. This study examines whether age at first exposure to abuse is associated with subsequent depression and suicidal ideation. Methods Data were drawn from the National Longitudinal Study of Adolescent Health (n = 15,701). Timing of first maltreatment exposure was classified using: (1) a crude measure capturing early childhood (ages 0–5), middle childhood (ages 6–10), or adolescence (ages 11–17); and (2) a refined measure capturing infancy (ages 0–2), preschool (ages 3–5), latency (ages 6–8), prepubertal (ages 9–10), pubertal (ages 11–13), or adolescence (ages 14–17). We examined whether timing of first exposure was associated with depression and suicidal ideation in early adulthood in the entire sample and among those exposed to maltreatment. Results Respondents exposed to abuse, particularly physical abuse, at any age had a higher odds of depression and suicidal ideation in young adulthood than nonmaltreated respondents. Among maltreated respondents, exposure during early childhood (ages 0–5), particularly preschool (ages 3–5), was most strongly associated with depression. Respondents first exposed to physical abuse during preschool had a 77% increase in the odds of depression and those first exposed to sexual abuse during early childhood had a 146% increase in the odds of suicidal ideation compared to respondents maltreated as adolescents. Conclusions Developmental timing of first exposure to maltreatment influences risk for depression and suicidal ideation. Whether these findings are evidence for biologically based sensitive periods requires further study.