We evaluated ruxolitinib in 65 patients with myelofibrosis according to age, sex, time of diagnosis, grade of fibrosis, prognostic score risk, Janus kinase (JAK) status, primary or secondary myelofibrosis, previous treatment, and dosage. Outcome measures were response rate, time to response, duration of response, and event-free survival and survival. Kaplan and Meier curves show a significant difference in event-free survival according to the prognostic score, in favor of patients with low int1 (p = 0.0009). The Cox stepwise model confirmed the result, the int2 high-risk score being the most powerful negative independent parameter (0.001), followed by JAK (0.008); other parameters, such as diagnosis more than 5 years earlier, grade III-IV fibrosis, and ruxolitinib dose have a negligible impact. Time to response was shorter (p = 0.001) in primary myelofibrosis. In conclusion, ruxolitinib is effective, with a better outcome in patients with a low-int1 risk score. This may suggest considering an earlier administration in the disease course.