Termination of breastfeeding in the first six months after childbirth is frequently caused by breastfeeding-related diseases and problems of the breast such as pain, milk stasis or mastitis. The aim of this study was to evaluate the relationship between psychological stress and the occurrence of breastfeeding associated disorders. In a prospective cohort study of 379 primiparous women without breast anomalies or diseases, psychometric data were collected from participants between the confirmation of the pregnancy and one year post-partum. Primarily, standardised questionnaires (PSQ, WHO QoL and F-SOZU K22) were used for data analysis while additional data was gathered in follow-up interviews. The subgroup analysis showed a significant relationship between stress and breastfeeding-related diseases. Women with pain, cracked nipples, milk stasis or mastitis reported a higher stress level than women without breast problems. Additionally, the majority of women with breast problems and increased psychological stress gave up breastfeeding sooner and, in contrast to the group without problems, indicated significantly more frequently that the milk quantity was insufficient. Breast diseases during lactation are associated with higher levels of psychological stress. Further studies are needed to examine the causes of the higher stress in order to develop strategies to prolong breastfeeding duration.