The purpose of the study was to evaluate psychological comorbidity in drug-naive or drug-free primary restless legs syndrome (p-RLS) patients with nocturnal eating disorder (NED), and to analyze the association of comorbid p-RLS and NED with obsessive-compulsive, mood and anxiety symptoms, and personality. Participants comprised 20 consecutive female outpatients with p-RLS, 10 without NED and 10 with NED, and 10 female controls matched for age. Both patients and controls were evaluated by the Hamilton Depression and the Anxiety Rating Scales, the State-Trait Anxiety Inventory, the Maudsley Obsessive Compulsive Inventory and the temperament and character inventory-revised. Compared to controls, p-RLS patients without and with NED had higher trait anxiety and current anxiety and obsessive-compulsive symptoms. p-RLS patients with NED also had significantly higher doubting compared to p-RLS patients without NED. Furthermore, groups differed for harm avoidance (HA), with p-RLS patients with and without NED having higher scores than controls. Untreated p-RLS patients, particularly those with nocturnal eating, report anxiety and obsessive-compulsive symptoms, perceive stressful situations as dangerous and threatening and tend to respond with anxiety to such situations. They have higher tendency to respond intensely to aversive stimuli, inhibiting behavior to avoid punishment, novelty, and frustrative omission of expected rewards. We hypothesize that higher levels of HA, a biologically determined personality trait, might constitute a diathesis predisposing individuals to display obsessive-compulsive symptoms, namely increasingly severe compulsive nocturnal eating.