Please post a photo and describe how often you water, what type of fertilizer you use, if it is in a container - the type of soil mix.

I have used both soil and fertilizer for a long time, and they are what you can get in Sweden (where I live) for Citrus, but I have a feeling it could be the fertilizer. I may change the soil comepletely today.... I'm ever so thankfull for your help.

Probably copper deficiency. See here a good guide for citrus: http://www.haifa-group.com/files/Guides/Citrus.pdf , look at the page 23.

When it happened to me, I have cut back the affected branches, because they will never grow normal again.

You might find this helpful: https://edis.ifas.ufl.edu/pdffiles/SS/SS42200.pdf

Note that it says : Excessive applications of N fertilizers have

been considered for years as a contributing cause of this problem,

Thank you ever so much for your help. After reading both of the studies your so helpfully adviced, I am convinced I have used too much fertilizer and that the fertilizer I normally use does not have the right balance of N and Cu. One of three new twigs I have had to cut off but after watering (with no fertilizer) the two other seem healthy. So it seems like I am back on track.

As you can only grow citrus in pots indoor in Sweden the market for soil and fertilizers are limited to just one brand.

I will try to import a more suitable fertilizer.

This tree means the world to mee. My son planted the seed when he was three years old and I regard it as his. He got really ill from lung tumor five years ago but is now declared a healty 26 year old. Even so I cannot get rid of the thought that keeping his tree alive keeps him alive.

:-)