The perinatal period is increasingly recognized as a vulnerable time for the development and exacerbation of psychiatric symptoms. Research has often focused on perinatal depression, with much less information on perinatal anxiety. This study examined the psychometric structure of all internalizing (anxiety and mood disorder symptoms) in the perinatal period. Participants were primarily community adults receiving prenatal care from an academic medical center (N = 246). Participants completed a structured clinical interview using the Interview for Mood and Anxiety Symptoms (IMAS) during pregnancy (28-32 weeks gestation) and the postpartum (6-8 weeks). Clinical interviews dimensionally assessed all current anxiety, mood, and obsessive-compulsive symptoms as well as lifetime psychiatric diagnoses. Confirmatory factor analyses identified three latent factors onto which psychiatric symptoms loaded: Distress (depression, generalized anxiety, irritability, and panic symptoms), Fear (social anxiety, agoraphobia, specific phobia, and obsessive-compulsive symptoms), and Bipolar (mania and obsessive-compulsive symptoms) in both pregnancy and the postpartum. The fit statistics of the models indicated adequate to good fit in both models. The IMAS is validated against the DSM-IV-TR rather than the DSM-5 and assessments of psychiatric symptoms were focused only on the current pregnancy. A three-factor model consisting of Distress, Fear and Bipolar latent factors was the best-fitting model in pregnancy and the postpartum period and showed stability across time. The structure of internalizing symptoms has important implications for future perinatal research and can be utilized to guide treatment by highlighting which psychiatric symptoms may be most similar during the perinatal period.