In diverticulosis or diverticular disease, the pressure inside the intestine causes the lining to bulge through the muscular layer, forming pouches, or diverticula, in the intestine wall. When there are dozens of diverticula, it is referred to as diverticulosis. On the other hand, if these diverticula get inflamed, it is referred to as diverticulitis.

Diverticula usually form gradually over several years. Disposition for diarrhoea, obesity, smoking, a low-fibre diet, and little exercise increase the risk of diverticula developing. Up to half of older than middle-aged people have diverticulosis or diverticula. Left-sided abdominal pain may indicate the inflammation of the diverticula, i.e. diverticulitis. In most cases, diverticulosis is symptom-free. Approximately a fifth of the people suffering from diverticulosis develop symptoms such as constipation, bloating, flatulence and abdominal pain, which often ease after defecating. In other words, the symptoms are very similar to IBS, i.e. Irritable Bowel Syndrome. Of course, a patient may have diverticulitis and IBS simultaneously. Diverticula can also cause heaving bleeding, chronic pain and constrictions. A diagnosis is made based on symptomatology, and it can be confirmed with imaging. Imaging is not necessary in all cases, but it is imperative when severe symptoms are involved and the CRP levels are elevated for the first time.