BackgroundDiagnosis of breast cancer in young women has been shown to affect their decision‐making with regard to fertility and family planning. Limited data are available from populations across the U.S. regarding this issue; thus, we sought to describe fertility concerns and efforts to preserve fertility in a national clinical trial population of young breast cancer patients.MethodsThe young and strong study was a cluster‐randomized controlled trial testing an intervention program for young women with breast cancer. Patients were surveyed within 3 months after diagnosis and at 3, 6, and 12 months after. Surveys asked about sociodemographics, psychosocial domains, fertility concerns, and fertility preservation strategies. Univariable and multivariable models were used to investigate sociodemographic, clinical, and psychosocial predictors of fertility concerns.ResultsOf 467 women from 54 clinical sites across the U.S. (14 academic, 40 community), 419 were evaluable regarding fertility concerns. Median age was 40 years (range 22–45), 11% were Black, 6% Hispanic, and 75% had children. Tumor stage was I (35%), II (51%), or III (14%); 82% received chemotherapy. At time of the treatment decision, 133 (32%) participants had fertility concerns, among whom 47% indicated this affected their treatment decisions. Sixty percent of participants reported having discussed fertility with their physician. Twenty percent of those with fertility concerns used fertility preservation strategies. History of difficulty becoming pregnant and younger age were associated with higher odds of fertility concerns in multivariable modeling.ConclusionMany young women with newly diagnosed breast cancer are concerned about fertility in a way that impacts their treatment decisions. Concerns were discussed, but few used fertility preservation strategies. These findings have implications for counseling young patients.