Negative mood states are characterized by both stress hormone dysregulation and serotonergic dysfunction, reflected by altered thalamic serotonin transporter (5-HTT) levels. However, so far, no study examined the individual association between cortisol response and cerebral in vivo 5-HTT levels in patients suffering from negative mood states.The objective of this cross-sectional study was to assess the interrelation of cortisol response, thalamic 5-HTT levels, and anxiety in healthy subjects and two previously published samples of patients with unipolar major depression (UMD) and obsessive-compulsive disorder (OCD), controlling for age, gender, 5-HTT genotype, smoking, and seasonality.Regional 5-HTT levels and cortisol response to dexamethasone-corticotropin (Dex-CRH) challenge were assessed in consecutive samples of medication-free patients suffering from UMD (N = 10) and OCD (N = 10), and 20 healthy volunteers. The intervention used was combined Dex-CRH test and [(11)C]DASB positron emission tomography. The main outcome measures were: 5-HTT binding potential (BP(ND)) in a predefined thalamic ROI, cortisol response defined as the maximum cortisol increase in the combined Dex-CRH-test, and state of anxiety from the state-trait-anxiety inventory.Reduced thalamic 5-HTT BP(ND) was associated with increased cortisol response (r = -0.35, p < 0.05; in patients: r = -0.53, p < 0.01) and with increased state anxiety (r = -0.46, p < 0.01), surviving correction for age, gender, 5-HTT genotype, smoking, and seasonality (p < 0.05). The 5-HTT genotype, on the contrary, was not significantly associated with cortisol response (p = 0.19) or negative mood (p = 0.23).The association between stress hormone response, thalamic 5-HTT levels, and anxiety in patients suffering from negative mood states suggests an interaction between two major mechanisms implicated in negative mood states in humans.