Pre-existing conditions don’t prevent recovery but require proving the accident aggravated or accelerated your underlying condition beyond its natural progression. Success depends on clear medical documentation showing your condition’s stability before the accident and deterioration afterward. Treating physicians who knew your pre-existing condition can provide crucial testimony about trauma-induced changes. Insurance companies aggressively investigate medical histories seeking pre-existing conditions to deny or minimize claims. Honesty about prior injuries prevents credibility damage while allowing your attorney to distinguish new harm from old problems. Diagnostic imaging comparing pre and post-accident conditions provides objective evidence of new injuries or worsening. The “eggshell plaintiff” doctrine protects recovery rights even when pre-existing conditions make you more susceptible to injury. Cases succeed by focusing on the defendant taking victims as they find them rather than denying compensation for vulnerabilities.