Background: Acid sphingomyelinase deficiency (ASMD) is a rare, progressive lysosomal storage disease with heterogeneous clinical manifestations. Evidence on the disease burden of ASMD is limited in Brazil. Methods: This observational, multicenter, retrospective study assessed the characteristics and clinical data of patients with ASMD type B and type A/B. Patients’ demographic data were retrieved from Hospital de Clínicas de Porto Alegre between January 1, 1986 and May 31, 2021, and available medical records were collected from eight centers in Brazil. Results: The study included 124 patients (full cohort: ASMD type B [75.8%] and type A/B [24.2%]; median [interquartile range {IQR}] age: 10.0 [3.6–19.9] years at diagnosis, n = 94), while medical records were available for 24 patients (subset cohort: ASMD type B [87.5%] and type A/B [12.5%]; median [IQR] age: 6.7 [1.9–11.3] years at diagnosis). Hepatobiliary and splenic manifestations were the most common clinical findings at symptom onset/diagnosis (75.0% and 70.8%, respectively) and at the last follow-up/death (83.3% each), with the majority of patients showing abnormal liver function parameters at both time points. At least 50.0% of patients had comorbidities at symptom onset or diagnosis. The incidence of hospitalization was reported in 33.3% patients at symptom onset/diagnosis and in 45.9% at the last follow-up/death. During the follow-up period, two patients with ASMD type A/B died in the subset cohort. Conclusions: The study provides insights into the high burden of illness in patients with ASMD, highlighting the need for disease awareness and early diagnosis in Brazil.