Introduction: Often considered the preserve of the elderly, particularly among women, stroke also affects young people, and neurologists are encountering this issue with increasing frequency in their daily practice. The objective of this study was to analyze trends in the incidence and prognosis of strokes in people under 55 years of age, by sex, as well as the causes of cerebral infarcts in this age group. Methods: All cases of stroke (cerebral infarcts, intracerebral hemorrhages, and undetermined strokes) among residents of Dijon were prospectively recorded from 1985 to 2011 in the Dijon Stroke Registry. Incidence rates among individuals under 55 years of age were calculated by sex, and temporal variations were analyzed using Poisson regression to estimate incidence rate ratios (IRR). Three-month survival was analyzed using Kaplan-Meier curves. Finally, the distribution of causes of cerebral infarction was classified according to the TOAST classification. Results: 4,506 patients with a first stroke were registered, of whom 453 (10.1%) were under 55 years of age (215 women and 238 men). Among these young patients, 375 (82.7%) were cerebral infarcts, 74 (16.3%) were intracerebral hemorrhages, and 3 (0.9%) were undetermined. The proportion of young patients among all stroke cases was 9% in 1985–1993, 9% in 1994–2002, and 11.8% in 2003–2011. The annual incidence of stroke among those under 55 years of age was 13.7 per 100,000 for women and 16.1 per 100,000 for men. The incidence increased over time by the same magnitude in both sexes. This increase is explained by a rise in the incidence of cerebral infarcts (IRR: 1.308; 95% CI: [0.982–1.741]; p = 0.066 for the 1994–2002 period and IRR: 2.220; 95% CI: [1.710–2.881]; p > 0.001 for the 2003–2011 period compared to the 1985–1993 reference period). An improvement in 3-month survival was observed over time among women (85.2% in 1985–1993, 96.8% in 1994–2002, and 96.8% in 2003–2011) as well as among men (85% in 1985–1993, 94% in 1994–2002, and 96.5% in 2003–2011) (>0.001 for the linear trend). Finally, regarding the etiology of cerebral infarcts, no cause was identified in one-third of cases; various causes were the most common (22%), including cervical arterial dissections, which accounted for 13.3% of cases. Conclusion: Stroke is not uncommon in young people, and its incidence has increased similarly in both women and men. Primary vascular prevention is necessary from an early age, through increased public information and education. Advances in patient care have led to improved survival rates in both sexes. Finally, the cause of cerebral infarction in young people remains unknown in a significant proportion of cases.