Objective Literature on patient-reported outcomes (PRO) of carcinoid syndrome symptoms (CSS) is scarce. We used a patient-reported outcome measure (PROM) to evaluate CSS, the domains of daily life impacted by CSS, the main symptoms that affect daily life, its change according to clinical, biological and morphological evolution, and the risk factors for a poor PRO-CSS score. Methods Patients completed the PRO-CSS, EORTC-QLQ30, and GI-NET21 questionnaires at the time of their clinical, laboratory, and morphological assessments in a multicentre French cohort study from February 2019 to May 2020. Results In total, 147 patients with metastatic ileal ( n =126), lung ( n =20), or unknown primitive neuroendocrine tumour but high 5-hydroxyindole-3-acetic acid level ( n =1) were included; 42 (32%) received an above-label dose of somatostatin analogues. Fifty-one (35%) patients had a poor PRO-CSS score. Travelling and food restriction were the two main domains affected. Diarrhoea (mean: 2.3/5 on Likert scale), imperiousness (mean of 2.5/5), fatigue (2.2/5), abdominal pain (1.7/5), and flushing episodes (1.5/5) were the main symptoms affecting daily life. The PRO-CSS score was not correlated to the clinical assessment performed by physicians at the baseline and during the follow-up. Patients with a poor PRO-CSS score had a higher tumour burden. Conclusions PROM-CSS may help physicians make an objective assessment of CSS and its impact in daily practice; this tool could become a key evaluation criterion in clinical trials focusing on CSS.