Background The aim of the present study was to assess sociodemographic and clinical differences between inpatients with major mood disorders (bipolar disorder - BD - and major depression - MDD) and the cyclothymic phenotype (CYC), and pure BDs or MDDs. Methods Participants were 281 adult inpatients (134 men and 147 women) consecutively admitted to the Department of Psychiatry of the Sant'Andrea University Hospital in Rome, Italy, between January 2008 and June 2010. The patients completed the Hamilton Scale for Depression (HAMD17), the Young Mania Rating Scale, the TEMPS-A (Temperament Evaluation of the Memphis, Pisa, Paris and San Diego - Autoquestionnaire), and the Beck Hopelessness Scale. Results 38.7% of the MDD patients and 48.3% of the BD patients satisfied criteria to be included in the cyclothymic groups. Above 92% of the patients with the cyclothymic phenotype reported suicidal ideation at the item #3 of the HAMD17. Furthermore, patients with the cyclothymic phenotype reported higher hopelessness than other patients. Limitations Our results are potentially limited by the small number of MDD-CYC patients included in the sample. Conclusions Our results support the clinical usefulness of the concept of soft bipolar spectrum. Patients with the cyclothymic phenotype differ from pure MDD patients and BD patients for temperamental profile and clinical variables.