Background: The birth and hospitalisation of a premature infant in a neonatal intensive care unit (NICU) are stressful experiences for the mother and the family. The support of neonatal nurses is necessary to control and reduce the stress of mothers. And nurse–parent support may play a role in effective stress management and make a positive contribution to the health of mothers. Aim: To determine the correlation of stress and nurse–parent support levels with mothers’ age and educational status, number of children, gestational week of the infant and the hospitalisation period of the infant among mothers of premature infants hospitalised in the NICU. Methods: This descriptive and cross-sectional study was conducted in the NICUs of two medical faculties. The study was conducted between March and June 2017 with the participation of 106 mothers with hospitalised premature infants. The data of the study were collected using a ‘mother information form’, Parental Stressor Scale: Neonatal Intensive Care Unit and Nurse-Parent Support Tool. Number, percentage, mean, standard deviation, t-test, analysis of variance test, Pearson's correlation and multiple regression analysis were used to analyse the data. Results: It was determined that the stress levels were high in mothers regarding their PSS: NICU parental role subscale. The stress levels of mothers with infants connected to mechanical ventilation and fed parenterally were high (p < 0.05). The nurse support levels of mothers with middle- and low-income status were high. Multiple regression analysis, mechanical ventilation was determined to be effective in the use of the PSS:NICU total score (p < 0.05). Conclusions: As a result, it was determined that mechanical ventilation and parenteral nutrition of the infant increased the stress level of mothers. Furthermore, in the study, the Nurse-Parent Support score of the mothers with middle- and low-income status was higher.