Henoch-Schönlein purpura (HSP) primarily affects children, but age at onset is thought to be important in determining disease severity and outcome. This study compared the clinical and laboratory data from children and adults with HSP. Methods: This retrospective 5-year study enrolled 65 children and 22 adult HSP patients attending a medical center. Results: Gross hematuria and lower-extremity edema were significantly more frequent in adults (p < 0.05). All the children developed renal involvement within 2 weeks, while 67% of the adult patients developed hematuria by the fifth week of disease onset. Elevated white blood cell count and increased erythrocyte sedimentation rate were significantly more common in children (p < 0.05). Adults had a higher frequency of renal involvement (p < 0.05), though this was also present in 14 children (21.54%), 12 with isolated hematuria and proteinuria and two with nephrotic syndrome. All the children maintained normal renal function. Twelve adults had renal involvement (52.6%), six with progression to renal insufficiency. Patients with abdominal pain at disease onset had a significantly higher probability of developing nephrotic syndrome (p < 0.05). Logistic regression revealed that age > 20 years, male, bloody stools, clinical course with relapse of purpuric rash, and persistent rash for > 1 month were poor prognostic indicators for HSP nephritis (p < 0.05). Conclusions: HSP nephritis in adults had a higher risk of progression to renal insufficiency. More aggressive treatment and extended follow-up with repeated urinalysis for at least 6 weeks were often necessary, especially in older patients.