OBJECTIVE: Pertussis is a highly contagious respiratory tract infection disease caused by Bordetella pertussis. Most severe cases occur in small infants. The clinical symptoms in infants may differ from older children, which cause difficulty in diagnosing pertussis in early infancy. This study aims to describe the characteristics of pediatric patients with probable pertussis, including cases in young infants. METHOD: We conducted a descriptive study that reviewed medical records of patients diagnosed with probable pertussis according to CDC guidelines that were admitted between April 2018 and March 2019 at the pediatric ward of Mohammad Hoesin Hospital. Patient's demographic characteristics and clinical symptoms were analyzed with chi-square test. RESULT: Thirty patients with probable pertussis were identified. Incidence rates were similar in both genders. Median age was 3.87(1-57) months with 18 patients aged <3 months, seven between 3 and 6 months, and only five aged >6 months. All had paroxysmal cough. Median duration of cough before admission was 10(1-40) days. Inspiratory whoop, posttussive vomiting, apnea, and seizure were found on 22(73.3%), 17(56.7%), 17(56.7%), and 6(20%) patients respectively. Apnea (13/17; p=0.035) and seizure (5/6; p=0.192) predominantly occurred in children under three months old. Pneumonia was comorbid with 80% cases. Possible source of transmission was identified on 56.7% of patient. Median length of hospital stay was 7(1-29) days, 6.7% of all admitted died. CONCLUSION: Children under three months were the most common group identified. Younger children tended to have more severe manifestations such as apnea and seizure. More than half of cases in this series had identifiable possible sources of transmission; thus, proper prevention and treatment are essential to reduce the risk of transmission to young children and infants.