Background: Motor retardation is a cardinal feature in adult depression. Limited information exists about motor activity in depressed children. The present study evaluated motor activity in depressed children compared to controls and investigated whether motor activity can be linked with the severity of symptoms in depressed children. Method: Motor activity during both day- and night time was recorded by actigraphy in twenty-two depressed children and their controls. A K-SADS-PL interview of the child and his/her mother was used to diagnose depression. The depressed children filled in the Child Depression Inventory (CDI) as a self-report of the severity of depression. Parents and teachers of both depressed children and controls filled in the Child Behavior Checklist (CBCL) and the Teacher Report Form (TRF). Results: Motor activity was reduced during the daytime in depressed children compared to controls ( p < 0.001). Depressed children spent more time in total immobility during the night time than their peers (p < 0.05). In depressed children motor activity was linked with the severity of self- (r = 0.45, p < 0.05) and teacher-reported (r = -0.52, p<0.05) symptoms. Depressed children with suicidal ideation (n = 10) differed significantly in motor activity compared to depressed children without suicidal ideation (n = 12) and controls (n = 22). Limitations: Sample size was only moderate. Conclusions: Reduced motor activity is an important feature of childhood depression. Objectively measured motor activity can distinguish depressed children from their peers. Motor retardation can be linked with the severity of depression, especially suicidal ideation and possibly subtype depressed children into groups with different etiology, treatment needs and course of illness. (C) 2011 Elsevier B.V. All rights reserved.