1、disease 泛指各种原因已查明的急性或慢性疾病，又可指传染病，甚至动植物的各种病害，概念十分广泛。如：

an acute disease 急性病

a chronic disease 慢性病

plant diseases 植物病害

His suffering is caused by the wound and not by the disease. 他的痛苦是由创伤而非疾病所引起的。

The ultimate causes of cancer and other diseases are still unknown.

癌症与其他某些疾病的根本原因始终不明。

2、illness 泛指疾病，极为普通常用，多指慢性病，或身体的极度虚弱等，但不影响日常的活动。它有时可与disease 交替使用。如：

There has been a lot of illness in the family recently. 最近以来这家人常生病。

An illness that caused him little difficulty in his youth began to take its toll as he reached middle age.

有种病在他年轻时影响并不大，但等他到了中年，却成了他的负担。