Importance: Pediatric palliative care treats patients with a wide variety of advanced illness conditions, often with substantial levels of pain and other symptoms. Clinical and research advancements regarding symptom management for these patients are hampered by the scarcity of data on symptoms as well as an overreliance on clinician report. Objective: To provide a detailed description of the symptoms among patients receiving pediatric palliative care based on parental report via a validated, structured symptom assessment measure. Design, Setting, and Participants: Baseline data for this cross-sectional analysis were collected between April 10, 2017, and February 5, 2020, from pediatric palliative care programs in 7 children's hospitals located in Akron, Ohio; Boston, Massachusetts; Birmingham, Alabama; Houston, Texas; Minneapolis, Minnesota; Philadelphia, Pennsylvania; and Seattle, Washington. Data were collected in the hospital, outpatient, and home setting from patients 30 years of age or younger who were receiving pediatric palliative care at 1 of the study sites. Exposures: Analyses were stratified by patients' demographic characteristics, including age, and by whether the patients had received a diagnosis of any of 10 non-mutually exclusive complex chronic condition categories. Main Outcomes and Measures: Twenty symptoms measured via the modified Memorial Symptom Assessment Scale, which scores the frequency and severity of any symptom that is present and provides a total symptom score. Results: Among the first 501 patients enrolled, the median age was 4.1 years (interquartile range, 0.8-12.9 years), 267 (53.3%) were male, and 356 (71.1%) were White. The most prevalent complex chronic conditions included gastrointestinal (357 [71.3%]), neurologic (289 [57.7%]), and cardiovascular (310 [61.9%]) conditions; 438 patients (87.4%) were technology dependent. Parents reported a mean (SD) of 6.7 (3.4) symptoms per patient and a median of 7 symptoms (interquartile range, 4-9 symptoms). A total of 367 patients (73.3%) had 5 or more symptoms. The 5 most prevalent symptoms were pain (319 [63.7%]; 95% CI, 59.4%-67.8%), lack of energy (295 [58.9%]; 95% CI, 54.5%-63.1%), irritability (280 [55.9%]; 95% CI, 51.5%-60.2%), drowsiness (247 [49.3%]; 95% CI, 44.9%-53.7%), and shortness of breath (232 [46.3%]; 95% CI, 41.9%-50.7%). Although older patients were reported by parents as having experienced more symptoms and having higher total symptom scores, variation across condition categories was relatively minor. Patients in the upper 10th percentile of total symptom scores had a median of 12.0 symptoms (interquartile range, 11-13). Conclusions and Relevance: In this cross-sectional study, most children receiving palliative care were experiencing polysymptomatology. An important subgroup of patients frequently experienced numerous severe symptoms. Assessment and management of patients with polysymptomatology are critical aspects of pediatric palliative care..