失读症（英语：dyslexia、reading disorder、或 alexia、或是读写障碍，或称为难语症、诵读障碍、阅读障碍、），是一种学习困难的表现，对于阅读和书写文本具有困难, 但具有常人的智商。

症状的严重程度因人而异。其他的症状包括难以念出字词，难以拼出单字，无法专注阅读，难以连续书写以及无法在阅读时清楚念出字词，或是无法理解阅读的内容。这些症状最先往往在学校时发现。这些读写上的困难，并不是患者自己可以控制的，读写障碍患者对于学习的渴望，通常与普通人并无二致。

一般认为，先天基因因素与后天环境因素，都同时是造成读写困难的原因。有些则看似与家族史相关。罹患注意力失调症的患者，通常也较容易发生读写障碍，且往往算术障碍。如果成人开始出现相关症状，也许是脑部创伤、中风或失智症所导致。相关的病理机制与大脑处理语言的过程有关。诊断过程包括了检测患者的记忆、拼字能力、视力和阅读技巧等。诊断的过程中需先排除因为未受阅读教育或阅读教育品质不良所导致的阅读困难，或是患者可能具有的视听障碍。

Dyslexia, also known as reading disorder, is characterized by trouble with reading unrelated to problems with overall intelligence. Different people are affected to varying degrees. Problems may include difficulties in spelling words, reading quickly, writing words, "sounding out" words in the head, pronouncing words when reading aloud and understanding what one reads. Often these difficulties are first noticed at school. When someone who previously could read loses their ability, it is known as alexia. The difficulties are involuntary and people with this disorder have an unaffected desire to learn.